diff --git a/src/Makefile.am b/src/Makefile.am
index ec9b099..4f2a58d 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -21,5 +21,5 @@ libjansson_la_LDFLAGS = \
 
 if GCC
 # These flags are gcc specific
-AM_CFLAGS = -Wall -Wextra -Werror
+AM_CFLAGS = -Wall -Wextra -Wdeclaration-after-statement -Werror
 endif
diff --git a/src/error.c b/src/error.c
index 074a68e..a7c8cbb 100644
--- a/src/error.c
+++ b/src/error.c
@@ -18,10 +18,12 @@ void jsonp_error_init(json_error_t *error, const char *source)
 
 void jsonp_error_set_source(json_error_t *error, const char *source)
 {
+    size_t length;
+
     if(!error || !source)
         return;
 
-    size_t length = strlen(source);
+    length = strlen(source);
     if(length < JSON_ERROR_SOURCE_LENGTH)
         strcpy(error->source, source);
     else {