diff --git a/libyara/include/yara/limits.h b/libyara/include/yara/limits.h
index af30d55e9a..ae4d1ac1d5 100644
--- a/libyara/include/yara/limits.h
+++ b/libyara/include/yara/limits.h
@@ -65,4 +65,24 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #define LEX_BUF_SIZE                    8192
 
 
+// Maximum allowed split ID, also limiting the number of split instructions
+// allowed in a regular expression. This number can't be increased
+// over 255 without changing RE_SPLIT_ID_TYPE.
+#define RE_MAX_SPLIT_ID                 128
+
+// Maximum stack size for regexp evaluation
+#define RE_MAX_STACK                    1024
+
+// Maximum code size for a compiled regexp
+#define RE_MAX_CODE_SIZE                32768
+
+// Maximum input size scanned by yr_re_exec
+#define RE_SCAN_LIMIT                   4096
+
+// Maximum number of fibers
+#define RE_MAX_FIBERS                   1024
+
+// Maximum number of levels in regexp's AST
+#define RE_MAX_AST_LEVELS               2000
+
 #endif
diff --git a/libyara/include/yara/re.h b/libyara/include/yara/re.h
index b421e9bc1e..ebdb1fd8e8 100644
--- a/libyara/include/yara/re.h
+++ b/libyara/include/yara/re.h
@@ -136,6 +136,7 @@ struct RE_NODE
 struct RE_AST
 {
   uint32_t flags;
+  uint16_t levels;
   RE_NODE* root_node;
 };
 
diff --git a/libyara/re.c b/libyara/re.c
index de20324ba7..959979ba28 100644
--- a/libyara/re.c
+++ b/libyara/re.c
@@ -52,23 +52,6 @@ order to avoid confusion with operating system threads.
 #include <yara/re_lexer.h>
 #include <yara/hex_lexer.h>
 
-// Maximum allowed split ID, also limiting the number of split instructions
-// allowed in a regular expression. This number can't be increased
-// over 255 without changing RE_SPLIT_ID_TYPE.
-#define RE_MAX_SPLIT_ID     128
-
-// Maximum stack size for regexp evaluation
-#define RE_MAX_STACK      1024
-
-// Maximum code size for a compiled regexp
-#define RE_MAX_CODE_SIZE  32768
-
-// Maximum input size scanned by yr_re_exec
-#define RE_SCAN_LIMIT     4096
-
-// Maximum number of fibers
-#define RE_MAX_FIBERS     1024
-
 
 #define EMIT_BACKWARDS                  0x01
 #define EMIT_DONT_SET_FORWARDS_CODE     0x02
@@ -268,6 +251,7 @@ int yr_re_ast_create(
     return ERROR_INSUFFICIENT_MEMORY;
 
   (*re_ast)->flags = 0;
+  (*re_ast)->levels = 0;
   (*re_ast)->root_node = NULL;
 
   return ERROR_SUCCESS;
diff --git a/libyara/re_grammar.c b/libyara/re_grammar.c
index 4122c7d48a..51839f6f00 100644
--- a/libyara/re_grammar.c
+++ b/libyara/re_grammar.c
@@ -88,6 +88,14 @@
 #define mark_as_not_fast_regexp() \
     ((RE_AST*) yyget_extra(yyscanner))->flags &= ~RE_FLAGS_FAST_REGEXP
 
+#define incr_ast_levels() \
+    if (((RE_AST*) yyget_extra(yyscanner))->levels++ > RE_MAX_AST_LEVELS) \
+    { \
+      lex_env->last_error_code = ERROR_INVALID_REGULAR_EXPRESSION; \
+      YYABORT; \
+    }
+
+
 #define ERROR_IF(x, error) \
     if (x) \
     { \
@@ -102,7 +110,7 @@
     } \
 
 
-#line 106 "re_grammar.c" /* yacc.c:339  */
+#line 114 "re_grammar.c" /* yacc.c:339  */
 
 # ifndef YY_NULLPTR
 #  if defined __cplusplus && 201103L <= __cplusplus
@@ -170,14 +178,14 @@ extern int re_yydebug;
 
 union YYSTYPE
 {
-#line 73 "re_grammar.y" /* yacc.c:355  */
+#line 81 "re_grammar.y" /* yacc.c:355  */
 
   int integer;
   uint32_t range;
   RE_NODE* re_node;
   uint8_t* class_vector;
 
-#line 181 "re_grammar.c" /* yacc.c:355  */
+#line 189 "re_grammar.c" /* yacc.c:355  */
 };
 
 typedef union YYSTYPE YYSTYPE;
@@ -193,7 +201,7 @@ int re_yyparse (void *yyscanner, RE_LEX_ENVIRONMENT *lex_env);
 
 /* Copy the second part of user declarations.  */
 
-#line 197 "re_grammar.c" /* yacc.c:358  */
+#line 205 "re_grammar.c" /* yacc.c:358  */
 
 #ifdef short
 # undef short
@@ -491,10 +499,10 @@ static const yytype_uint8 yytranslate[] =
   /* YYRLINE[YYN] -- Source line where rule number YYN was defined.  */
 static const yytype_uint16 yyrline[] =
 {
-       0,   104,   104,   109,   113,   117,   128,   146,   150,   161,
-     175,   191,   205,   221,   244,   268,   290,   313,   317,   323,
-     329,   335,   344,   348,   354,   362,   368,   374,   380,   386,
-     392,   398
+       0,   112,   112,   117,   121,   125,   137,   156,   160,   173,
+     187,   203,   217,   233,   256,   280,   302,   325,   329,   335,
+     341,   347,   356,   362,   368,   376,   382,   388,   394,   400,
+     406,   412
 };
 #endif
 
@@ -1039,33 +1047,33 @@ yydestruct (const char *yymsg, int yytype, YYSTYPE *yyvaluep, void *yyscanner, R
   switch (yytype)
     {
           case 6: /* _CLASS_  */
-#line 96 "re_grammar.y" /* yacc.c:1257  */
+#line 104 "re_grammar.y" /* yacc.c:1257  */
       { yr_free(((*yyvaluep).class_vector)); }
-#line 1045 "re_grammar.c" /* yacc.c:1257  */
+#line 1053 "re_grammar.c" /* yacc.c:1257  */
         break;
 
     case 26: /* alternative  */
-#line 97 "re_grammar.y" /* yacc.c:1257  */
+#line 105 "re_grammar.y" /* yacc.c:1257  */
       { yr_re_node_destroy(((*yyvaluep).re_node)); }
-#line 1051 "re_grammar.c" /* yacc.c:1257  */
+#line 1059 "re_grammar.c" /* yacc.c:1257  */
         break;
 
     case 27: /* concatenation  */
-#line 98 "re_grammar.y" /* yacc.c:1257  */
+#line 106 "re_grammar.y" /* yacc.c:1257  */
       { yr_re_node_destroy(((*yyvaluep).re_node)); }
-#line 1057 "re_grammar.c" /* yacc.c:1257  */
+#line 1065 "re_grammar.c" /* yacc.c:1257  */
         break;
 
     case 28: /* repeat  */
-#line 99 "re_grammar.y" /* yacc.c:1257  */
+#line 107 "re_grammar.y" /* yacc.c:1257  */
       { yr_re_node_destroy(((*yyvaluep).re_node)); }
-#line 1063 "re_grammar.c" /* yacc.c:1257  */
+#line 1071 "re_grammar.c" /* yacc.c:1257  */
         break;
 
     case 29: /* single  */
-#line 100 "re_grammar.y" /* yacc.c:1257  */
+#line 108 "re_grammar.y" /* yacc.c:1257  */
       { yr_re_node_destroy(((*yyvaluep).re_node)); }
-#line 1069 "re_grammar.c" /* yacc.c:1257  */
+#line 1077 "re_grammar.c" /* yacc.c:1257  */
         break;
 
 
@@ -1331,26 +1339,27 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
   switch (yyn)
     {
         case 2:
-#line 105 "re_grammar.y" /* yacc.c:1646  */
+#line 113 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast = yyget_extra(yyscanner);
         re_ast->root_node = (yyvsp[0].re_node);
       }
-#line 1340 "re_grammar.c" /* yacc.c:1646  */
+#line 1348 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 4:
-#line 114 "re_grammar.y" /* yacc.c:1646  */
+#line 122 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = (yyvsp[0].re_node);
       }
-#line 1348 "re_grammar.c" /* yacc.c:1646  */
+#line 1356 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 5:
-#line 118 "re_grammar.y" /* yacc.c:1646  */
+#line 126 "re_grammar.y" /* yacc.c:1646  */
     {
         mark_as_not_fast_regexp();
+        incr_ast_levels();
 
         (yyval.re_node) = yr_re_node_create(RE_NODE_ALT, (yyvsp[-2].re_node), (yyvsp[0].re_node));
 
@@ -1359,15 +1368,16 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1363 "re_grammar.c" /* yacc.c:1646  */
+#line 1372 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 6:
-#line 129 "re_grammar.y" /* yacc.c:1646  */
+#line 138 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_NODE* node;
 
         mark_as_not_fast_regexp();
+        incr_ast_levels();
 
         node = yr_re_node_create(RE_NODE_EMPTY, NULL, NULL);
 
@@ -1378,31 +1388,33 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1382 "re_grammar.c" /* yacc.c:1646  */
+#line 1392 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 7:
-#line 147 "re_grammar.y" /* yacc.c:1646  */
+#line 157 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = (yyvsp[0].re_node);
       }
-#line 1390 "re_grammar.c" /* yacc.c:1646  */
+#line 1400 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 8:
-#line 151 "re_grammar.y" /* yacc.c:1646  */
+#line 161 "re_grammar.y" /* yacc.c:1646  */
     {
+        incr_ast_levels();
+
         (yyval.re_node) = yr_re_node_create(RE_NODE_CONCAT, (yyvsp[-1].re_node), (yyvsp[0].re_node));
 
         DESTROY_NODE_IF((yyval.re_node) == NULL, (yyvsp[-1].re_node));
         DESTROY_NODE_IF((yyval.re_node) == NULL, (yyvsp[0].re_node));
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1402 "re_grammar.c" /* yacc.c:1646  */
+#line 1414 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 9:
-#line 162 "re_grammar.y" /* yacc.c:1646  */
+#line 174 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast;
 
@@ -1416,11 +1428,11 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
         DESTROY_NODE_IF((yyval.re_node) == NULL, (yyvsp[-1].re_node));
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1420 "re_grammar.c" /* yacc.c:1646  */
+#line 1432 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 10:
-#line 176 "re_grammar.y" /* yacc.c:1646  */
+#line 188 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast;
 
@@ -1436,11 +1448,11 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
 
         (yyval.re_node)->greedy = FALSE;
       }
-#line 1440 "re_grammar.c" /* yacc.c:1646  */
+#line 1452 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 11:
-#line 192 "re_grammar.y" /* yacc.c:1646  */
+#line 204 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast;
 
@@ -1454,11 +1466,11 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
         DESTROY_NODE_IF((yyval.re_node) == NULL, (yyvsp[-1].re_node));
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1458 "re_grammar.c" /* yacc.c:1646  */
+#line 1470 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 12:
-#line 206 "re_grammar.y" /* yacc.c:1646  */
+#line 218 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast;
 
@@ -1474,11 +1486,11 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
 
         (yyval.re_node)->greedy = FALSE;
       }
-#line 1478 "re_grammar.c" /* yacc.c:1646  */
+#line 1490 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 13:
-#line 222 "re_grammar.y" /* yacc.c:1646  */
+#line 234 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast = yyget_extra(yyscanner);
         re_ast->flags |= RE_FLAGS_GREEDY;
@@ -1501,11 +1513,11 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
         (yyval.re_node)->start = 0;
         (yyval.re_node)->end = 1;
       }
-#line 1505 "re_grammar.c" /* yacc.c:1646  */
+#line 1517 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 14:
-#line 245 "re_grammar.y" /* yacc.c:1646  */
+#line 257 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast = yyget_extra(yyscanner);
         re_ast->flags |= RE_FLAGS_UNGREEDY;
@@ -1529,11 +1541,11 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
         (yyval.re_node)->end = 1;
         (yyval.re_node)->greedy = FALSE;
       }
-#line 1533 "re_grammar.c" /* yacc.c:1646  */
+#line 1545 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 15:
-#line 269 "re_grammar.y" /* yacc.c:1646  */
+#line 281 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast = yyget_extra(yyscanner);
         re_ast->flags |= RE_FLAGS_GREEDY;
@@ -1555,11 +1567,11 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
         (yyval.re_node)->start = (yyvsp[0].range) & 0xFFFF;;
         (yyval.re_node)->end = (yyvsp[0].range) >> 16;;
       }
-#line 1559 "re_grammar.c" /* yacc.c:1646  */
+#line 1571 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 16:
-#line 291 "re_grammar.y" /* yacc.c:1646  */
+#line 303 "re_grammar.y" /* yacc.c:1646  */
     {
         RE_AST* re_ast = yyget_extra(yyscanner);
         re_ast->flags |= RE_FLAGS_UNGREEDY;
@@ -1582,77 +1594,79 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
         (yyval.re_node)->end = (yyvsp[-1].range) >> 16;;
         (yyval.re_node)->greedy = FALSE;
       }
-#line 1586 "re_grammar.c" /* yacc.c:1646  */
+#line 1598 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 17:
-#line 314 "re_grammar.y" /* yacc.c:1646  */
+#line 326 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = (yyvsp[0].re_node);
       }
-#line 1594 "re_grammar.c" /* yacc.c:1646  */
+#line 1606 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 18:
-#line 318 "re_grammar.y" /* yacc.c:1646  */
+#line 330 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_WORD_BOUNDARY, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1604 "re_grammar.c" /* yacc.c:1646  */
+#line 1616 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 19:
-#line 324 "re_grammar.y" /* yacc.c:1646  */
+#line 336 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_NON_WORD_BOUNDARY, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1614 "re_grammar.c" /* yacc.c:1646  */
+#line 1626 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 20:
-#line 330 "re_grammar.y" /* yacc.c:1646  */
+#line 342 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_ANCHOR_START, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1624 "re_grammar.c" /* yacc.c:1646  */
+#line 1636 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 21:
-#line 336 "re_grammar.y" /* yacc.c:1646  */
+#line 348 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_ANCHOR_END, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1634 "re_grammar.c" /* yacc.c:1646  */
+#line 1646 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 22:
-#line 345 "re_grammar.y" /* yacc.c:1646  */
+#line 357 "re_grammar.y" /* yacc.c:1646  */
     {
+        incr_ast_levels();
+
         (yyval.re_node) = (yyvsp[-1].re_node);
       }
-#line 1642 "re_grammar.c" /* yacc.c:1646  */
+#line 1656 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 23:
-#line 349 "re_grammar.y" /* yacc.c:1646  */
+#line 363 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_ANY, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1652 "re_grammar.c" /* yacc.c:1646  */
+#line 1666 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 24:
-#line 355 "re_grammar.y" /* yacc.c:1646  */
+#line 369 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_LITERAL, NULL, NULL);
 
@@ -1660,71 +1674,71 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
 
         (yyval.re_node)->value = (yyvsp[0].integer);
       }
-#line 1664 "re_grammar.c" /* yacc.c:1646  */
+#line 1678 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 25:
-#line 363 "re_grammar.y" /* yacc.c:1646  */
+#line 377 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_WORD_CHAR, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1674 "re_grammar.c" /* yacc.c:1646  */
+#line 1688 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 26:
-#line 369 "re_grammar.y" /* yacc.c:1646  */
+#line 383 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_NON_WORD_CHAR, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1684 "re_grammar.c" /* yacc.c:1646  */
+#line 1698 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 27:
-#line 375 "re_grammar.y" /* yacc.c:1646  */
+#line 389 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_SPACE, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1694 "re_grammar.c" /* yacc.c:1646  */
+#line 1708 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 28:
-#line 381 "re_grammar.y" /* yacc.c:1646  */
+#line 395 "re_grammar.y" /* yacc.c:1646  */
     {
          (yyval.re_node) = yr_re_node_create(RE_NODE_NON_SPACE, NULL, NULL);
 
          ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1704 "re_grammar.c" /* yacc.c:1646  */
+#line 1718 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 29:
-#line 387 "re_grammar.y" /* yacc.c:1646  */
+#line 401 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_DIGIT, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1714 "re_grammar.c" /* yacc.c:1646  */
+#line 1728 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 30:
-#line 393 "re_grammar.y" /* yacc.c:1646  */
+#line 407 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_NON_DIGIT, NULL, NULL);
 
         ERROR_IF((yyval.re_node) == NULL, ERROR_INSUFFICIENT_MEMORY);
       }
-#line 1724 "re_grammar.c" /* yacc.c:1646  */
+#line 1738 "re_grammar.c" /* yacc.c:1646  */
     break;
 
   case 31:
-#line 399 "re_grammar.y" /* yacc.c:1646  */
+#line 413 "re_grammar.y" /* yacc.c:1646  */
     {
         (yyval.re_node) = yr_re_node_create(RE_NODE_CLASS, NULL, NULL);
 
@@ -1732,11 +1746,11 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
 
         (yyval.re_node)->class_vector = (yyvsp[0].class_vector);
       }
-#line 1736 "re_grammar.c" /* yacc.c:1646  */
+#line 1750 "re_grammar.c" /* yacc.c:1646  */
     break;
 
 
-#line 1740 "re_grammar.c" /* yacc.c:1646  */
+#line 1754 "re_grammar.c" /* yacc.c:1646  */
       default: break;
     }
   /* User semantic actions sometimes alter yychar, and that requires
@@ -1964,5 +1978,5 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
 #endif
   return yyresult;
 }
-#line 407 "re_grammar.y" /* yacc.c:1906  */
+#line 421 "re_grammar.y" /* yacc.c:1906  */
 
diff --git a/libyara/re_grammar.h b/libyara/re_grammar.h
index c673bd131b..8ba1c56dec 100644
--- a/libyara/re_grammar.h
+++ b/libyara/re_grammar.h
@@ -78,7 +78,7 @@ extern int re_yydebug;
 
 union YYSTYPE
 {
-#line 73 "re_grammar.y" /* yacc.c:1909  */
+#line 81 "re_grammar.y" /* yacc.c:1909  */
 
   int integer;
   uint32_t range;
diff --git a/libyara/re_grammar.y b/libyara/re_grammar.y
index 9a22b44cfb..9e88d24e85 100644
--- a/libyara/re_grammar.y
+++ b/libyara/re_grammar.y
@@ -46,6 +46,14 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #define mark_as_not_fast_regexp() \
     ((RE_AST*) yyget_extra(yyscanner))->flags &= ~RE_FLAGS_FAST_REGEXP
 
+#define incr_ast_levels() \
+    if (((RE_AST*) yyget_extra(yyscanner))->levels++ > RE_MAX_AST_LEVELS) \
+    { \
+      lex_env->last_error_code = ERROR_INVALID_REGULAR_EXPRESSION; \
+      YYABORT; \
+    }
+
+
 #define ERROR_IF(x, error) \
     if (x) \
     { \
@@ -117,6 +125,7 @@ alternative
     | alternative '|' concatenation
       {
         mark_as_not_fast_regexp();
+        incr_ast_levels();
 
         $$ = yr_re_node_create(RE_NODE_ALT, $1, $3);
 
@@ -130,6 +139,7 @@ alternative
         RE_NODE* node;
 
         mark_as_not_fast_regexp();
+        incr_ast_levels();
 
         node = yr_re_node_create(RE_NODE_EMPTY, NULL, NULL);
 
@@ -149,6 +159,8 @@ concatenation
       }
     | concatenation repeat
       {
+        incr_ast_levels();
+
         $$ = yr_re_node_create(RE_NODE_CONCAT, $1, $2);
 
         DESTROY_NODE_IF($$ == NULL, $1);
@@ -343,6 +355,8 @@ repeat
 single
     : '(' alternative ')'
       {
+        incr_ast_levels();
+
         $$ = $2;
       }
     | '.'