diff --git a/jerry-libc/include/stdlib.h b/jerry-libc/include/stdlib.h
index dd802fa090..4682af8d55 100644
--- a/jerry-libc/include/stdlib.h
+++ b/jerry-libc/include/stdlib.h
@@ -33,6 +33,7 @@ void __attribute__ ((noreturn)) exit (int);
 void __attribute__ ((noreturn)) abort (void);
 int rand (void);
 void srand (unsigned int);
+long int strtol (const char *, char **, int);
 
 #ifdef __cplusplus
 }
diff --git a/jerry-libc/jerry-libc.c b/jerry-libc/jerry-libc.c
index 20c947c5b7..6511950594 100644
--- a/jerry-libc/jerry-libc.c
+++ b/jerry-libc/jerry-libc.c
@@ -17,6 +17,7 @@
  * Jerry libc's common functions implementation
  */
 
+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -280,3 +281,76 @@ srand (unsigned int seed) /**< new seed */
   libc_random_gen_state[2] =
   libc_random_gen_state[3] = seed;
 } /* srand */
+
+/**
+ * Convert a string to a long integer.
+ *
+ * The function first discards leading whitespace characters. Then takes an
+ * optional sign followed by as many digits as possible and interprets them as a
+ * numerical value. Additional characters after those that form the number are
+ * ignored.
+ *
+ * Note:
+ *      If base is not 10, the behaviour is undefined.
+ *      If the value read is out-of-range, the behaviour is undefined.
+ *      The implementation never sets errno.
+ *
+ * @return the integer value of str.
+ */
+long int
+strtol (const char *nptr, /**< string representation of an integer number */
+        char **endptr, /**< [out] the address of the first non-number character */
+        int base) /**< numerical base or radix (MUST be 10) */
+{
+  assert (base == 10);
+  (void) base; /* Unused. */
+
+  const char *str = nptr;
+
+  /* Skip leading whitespaces. */
+  while (*str == ' ' || *str == '\t' || *str == '\r' || *str == '\n')
+  {
+    str++;
+  }
+
+  bool digits = false;
+  bool positive = true;
+  long int num = 0;
+
+  /* Process optional sign. */
+  if (*str == '-')
+  {
+    positive = false;
+    str++;
+  }
+  else if (*str == '+')
+  {
+    str++;
+  }
+
+  /* Process base-10 digits. */
+  while (*str >= '0' && *str <= '9')
+  {
+    num = num * 10 + (*str - '0');
+    digits = true;
+    str++;
+  }
+
+  /* Set endptr and return result*/
+  if (digits)
+  {
+    if (endptr)
+    {
+      *endptr = (char *) str;
+    }
+    return positive ? num : -num;
+  }
+  else
+  {
+    if (endptr)
+    {
+      *endptr = (char *) nptr;
+    }
+    return 0L;
+  }
+} /* strtol */
diff --git a/jerry-main/main-unix.c b/jerry-main/main-unix.c
index 7586a4eb58..5f8f7e5ac5 100644
--- a/jerry-main/main-unix.c
+++ b/jerry-main/main-unix.c
@@ -126,30 +126,6 @@ jerry_value_is_syntax_error (jerry_value_t error_value) /**< error value */
   return false;
 } /* jerry_value_is_syntax_error */
 
-/**
- * Convert string into unsigned integer
- *
- * @return converted number
- */
-static uint32_t
-str_to_uint (const char *num_str_p) /**< string to convert */
-{
-  assert (jerry_is_feature_enabled (JERRY_FEATURE_ERROR_MESSAGES));
-
-  uint32_t result = 0;
-
-  while (*num_str_p != '\0')
-  {
-    assert (*num_str_p >= '0' && *num_str_p <= '9');
-
-    result *= 10;
-    result += (uint32_t) (*num_str_p - '0');
-    num_str_p++;
-  }
-
-  return result;
-} /* str_to_uint */
-
 /**
  * Print error value
  */
@@ -177,18 +153,18 @@ print_unhandled_exception (jerry_value_t error_value) /**< error value */
 
     if (jerry_is_feature_enabled (JERRY_FEATURE_ERROR_MESSAGES) && jerry_value_is_syntax_error (error_value))
     {
-      uint32_t err_line = 0;
-      uint32_t err_col = 0;
+      unsigned int err_line = 0;
+      unsigned int err_col = 0;
 
       /* 1. parse column and line information */
-      for (uint32_t i = 0; i < sz; i++)
+      for (jerry_size_t i = 0; i < sz; i++)
       {
         if (!strncmp ((char *) (err_str_buf + i), "[line: ", 7))
         {
           i += 7;
 
           char num_str[8];
-          uint32_t j = 0;
+          unsigned int j = 0;
 
           while (i < sz && err_str_buf[i] != ',')
           {
@@ -198,7 +174,7 @@ print_unhandled_exception (jerry_value_t error_value) /**< error value */
           }
           num_str[j] = '\0';
 
-          err_line = str_to_uint (num_str);
+          err_line = (unsigned int) strtol (num_str, NULL, 10);
 
           if (strncmp ((char *) (err_str_buf + i), ", column: ", 10))
           {
@@ -216,17 +192,17 @@ print_unhandled_exception (jerry_value_t error_value) /**< error value */
           }
           num_str[j] = '\0';
 
-          err_col = str_to_uint (num_str);
+          err_col = (unsigned int) strtol (num_str, NULL, 10);
           break;
         }
       } /* for */
 
       if (err_line != 0 && err_col != 0)
       {
-        uint32_t curr_line = 1;
+        unsigned int curr_line = 1;
 
         bool is_printing_context = false;
-        uint32_t pos = 0;
+        unsigned int pos = 0;
 
         /* 2. seek and print */
         while (buffer[pos] != '\0')
@@ -519,10 +495,12 @@ main (int argc,
       }
       case OPT_LOG_LEVEL:
       {
-        check_usage (strlen (cli_state.arg[1]) == 1 && cli_state.arg[1][0] >= '0' && cli_state.arg[1][0] <= '3',
+        char *endptr;
+        long int log_level = strtol (cli_state.arg[1], &endptr, 10);
+        check_usage (log_level >= 0 && log_level <= 3 && !*endptr,
                      argv[0], "Error: wrong format for ", cli_state.arg[0]);
 
-        jerry_port_default_set_log_level ((jerry_log_level_t) (cli_state.arg[1][0] - '0'));
+        jerry_port_default_set_log_level ((jerry_log_level_t) log_level);
         break;
       }
       case OPT_ABORT_ON_FAIL: