diff --git a/src/FileCheck.py b/src/FileCheck.py
index 90066b0..e3171e1 100755
--- a/src/FileCheck.py
+++ b/src/FileCheck.py
@@ -22,6 +22,14 @@ class CheckType(Enum):
 
 Check = namedtuple("Check", "check_type match_type expression source_line start_index")
 
+def dump_check(check):
+    print("check dump")
+    print("\tcheck_type: {}".format(check.check_type))
+    print("\tmatch_type: {}".format(check.match_type))
+    print("\texpression: {}".format(check.expression))
+    print("\tsource_line: {}".format(check.source_line))
+    print("\tstart_index: {}".format(check.start_index))
+
 # FileCheck always prints its first argument.
 print(sys.argv[0])
 
@@ -63,18 +71,30 @@ class CheckType(Enum):
                           start_index=check_match.start(1))
 
             checks.append(check)
+            continue
 
         check_match = re.search('; CHECK-NOT: (.*)', line)
         if check_match:
+            match_type = MatchType.SUBSTRING
+
             check_expression = check_match.group(1)
 
+            regex_line = re.sub(r"\{\{(.*?)\}\}", r"\1", check_expression)
+
+            if check_expression != regex_line:
+                match_type = MatchType.REGEX
+                check_expression = regex_line
+            else:
+                check_expression = re.sub("\\s+", ' ', check_expression).strip()
+
             check = Check(check_type=CheckType.CHECK_NOT,
-                          match_type=MatchType.SUBSTRING,
+                          match_type=match_type,
                           expression=check_expression,
                           source_line=line,
                           start_index=check_match.start(1))
 
             checks.append(check)
+            continue
 
         check_match = re.search('; CHECK-EMPTY:', line)
         if check_match:
@@ -91,6 +111,7 @@ class CheckType(Enum):
                 exit(2)
 
             checks.append(check)
+            continue
 
 check_iterator = iter(checks)
 
@@ -103,7 +124,12 @@ class CheckType(Enum):
     print("error: no check strings found with prefix 'CHECK:'", file=sys.stderr)
     exit(2)
 
+current_line = None
+current_line_number = 0
 for line in sys.stdin:
+    current_line = line
+    current_line_number += 1
+
     line_counter = 1
 
     if current_check.check_type == CheckType.CHECK_EMPTY:
@@ -117,10 +143,21 @@ class CheckType(Enum):
             if current_check.expression not in line:
                 continue
 
-        if current_check.match_type == MatchType.REGEX:
+        elif current_check.match_type == MatchType.REGEX:
             if not re.search(current_check.expression, line):
                 continue
 
+    if current_check.check_type == CheckType.CHECK_NOT:
+        if current_check.match_type == MatchType.SUBSTRING:
+            line = re.sub("\\s+", ' ', line).strip()
+
+            if current_check.expression in line:
+                break
+
+        elif current_check.match_type == MatchType.REGEX:
+            if re.search(current_check.expression, line):
+                break
+
     try:
         current_check = next(check_iterator)
     except StopIteration:
@@ -156,10 +193,21 @@ class CheckType(Enum):
         print(current_check.source_line.rstrip())
         print("          ^")
         print("<stdin>:?:?: note: scanning from here")
-        print("TODO")
+        print(line)
         print("^")
         exit(1)
 
-    # print("foo: {}".format(line == "\n"))
+if current_check.check_type == CheckType.CHECK_NOT:
+    if current_check.match_type == MatchType.SUBSTRING:
+        print("{}:{}:{}: error: CHECK-NOT: excluded string found in input"
+              .format(check_file, line_counter, current_check.start_index + 1))
 
+        print(current_check.source_line.rstrip())
+        print("^".rjust(current_check.start_index + 1))
+        print("<stdin>:?:?: note: found here")
+        print(current_line)
+        print("^".ljust(len(current_line), '~'))
+        exit(1)
 
+    if current_check.match_type == MatchType.REGEX:
+        assert 0, "Not implemented"
diff --git a/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/filecheck.check b/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/filecheck.check
new file mode 100644
index 0000000..920d6b1
--- /dev/null
+++ b/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/filecheck.check
@@ -0,0 +1 @@
+; CHECK-NOT: hello
\ No newline at end of file
diff --git a/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/filecheck.input b/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/filecheck.input
new file mode 100644
index 0000000..b6fc4c6
--- /dev/null
+++ b/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/filecheck.input
@@ -0,0 +1 @@
+hello
\ No newline at end of file
diff --git a/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/sample.itest b/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/sample.itest
new file mode 100644
index 0000000..e3cbd69
--- /dev/null
+++ b/tests/integration/tests/basic_functionality/check_commands/CHECK-NOT/one_string/01-negative_match/sample.itest
@@ -0,0 +1,9 @@
+; RUN: cat %S/filecheck.input | (%FILECHECK_EXEC %S/filecheck.check 2>&1; test $? == 1;) | %FILECHECK_TESTER_EXEC %s
+; CHECK: {{^.*}}FileCheck
+; CHECK-NEXT: {{^.*}}filecheck.check:1:14: error: CHECK-NOT: excluded string found in input{{$}}
+; CHECK-NEXT: {{^}}; CHECK-NOT: hello{{$}}
+; CHECK-NEXT: {{^}}             ^{{$}}
+; CHECK-NEXT: {{^<stdin>:.*:.*: note: found here$}}
+; CHECK-NEXT: {{^}}hello{{$}}
+; CHECK-NEXT: {{^}}^~~~~{{$}}
+; CHECK-EMPTY: