diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2930fe3fa8..9431ceac4f 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -273,6 +273,9 @@ project (Jerry C ASM)
   add_jerry_compile_warnings(all extra format-nonliteral init-self conversion sign-conversion format-security missing-declarations pedantic)
   add_jerry_compile_flags(-Wno-stack-protector -Wno-attributes)
   if(CMAKE_COMPILER_IS_GNUCC)
+    if(${USE_JERRY_LIBC})
+      add_jerry_compile_flags(-Werror)
+    endif()
     add_jerry_compile_warnings(logical-op)
   else()
     add_jerry_compile_flags(-Wno-nested-anon-types)
diff --git a/jerry-core/ecma/base/ecma-helpers-string.c b/jerry-core/ecma/base/ecma-helpers-string.c
index 19f65e9f5c..50384ba71d 100644
--- a/jerry-core/ecma/base/ecma-helpers-string.c
+++ b/jerry-core/ecma/base/ecma-helpers-string.c
@@ -918,7 +918,7 @@ ecma_compare_ecma_strings_relational (const ecma_string_t *string1_p, /**< ecma-
     return false;
   }
 
-  const lit_utf8_byte_t *utf8_string1_p, *utf8_string2_p;
+  lit_utf8_byte_t *utf8_string1_p, *utf8_string2_p;
   bool is_utf8_string1_on_heap = false, is_utf8_string2_on_heap = false;
   lit_utf8_byte_t utf8_string1_buffer[ECMA_MAX_CHARS_IN_STRINGIFIED_NUMBER];
   lit_utf8_size_t utf8_string1_size;