diff --git a/src/heap.c b/src/heap.c
index ba25e7e..e71b9ab 100644
--- a/src/heap.c
+++ b/src/heap.c
@@ -27,6 +27,8 @@
 #include "heap.h"
 #include "text.h"
 
+#ifndef NDEBUG
+
 void *debugging_calloc (size_t nmemb, size_t size, const char *file,
                         unsigned long line)
 {
@@ -91,6 +93,8 @@ char *debugging_strdup (const char *s, const char *file, unsigned long line)
         return ptr;
 }
 
+#endif /* !NDEBUG */
+
 /*
  * Allocate a block of memory in the "shared" memory region.
  *