diff --git a/runtime/Makefile b/runtime/Makefile
index d46f2a8a8..42ae89720 100644
--- a/runtime/Makefile
+++ b/runtime/Makefile
@@ -1,5 +1,5 @@
 CC=clang
-COMMON_FLAGS=-g2 -fstack-protector-all
+COMMON_FLAGS=-g2 -std=gnu99 -fstack-protector-all -Wimplicit-function-declaration
 PROD_FLAGS=$(COMMON_FLAGS) -DLAMA_ENV
 TEST_FLAGS=$(COMMON_FLAGS) -DDEBUG_VERSION
 UNIT_TESTS_FLAGS=$(TEST_FLAGS)
diff --git a/runtime/runtime.c b/runtime/runtime.c
index 0e865cd8f..73bd9f47a 100644
--- a/runtime/runtime.c
+++ b/runtime/runtime.c
@@ -476,10 +476,6 @@ extern void *Lsubstring (void *subj, aint p, aint l) {
   return NULL;
 }
 
-extern const char *re_compile_pattern (const char *__pattern, size_t __length,
-				       struct re_pattern_buffer *__buffer)
-    _Attr_access_ ((__read_only__, 1, 2));
-
 extern struct re_pattern_buffer *Lregexp (char *regexp) {
   regex_t *b = (regex_t *)malloc(sizeof(regex_t));
 
@@ -494,11 +490,6 @@ extern struct re_pattern_buffer *Lregexp (char *regexp) {
   return b;
 }
 
-extern regoff_t re_match (struct re_pattern_buffer *__buffer,
-			  const char *__String, regoff_t __length,
-			  regoff_t __start, struct re_registers *__regs)
-    _Attr_access_ ((__read_only__, 2, 3));
-
 extern aint LregexpMatch (struct re_pattern_buffer *b, char *s, aint pos) {
   aint res;