diff --git a/src/zmalloc.c b/src/zmalloc.c
index 0d360779..f653760a 100644
--- a/src/zmalloc.c
+++ b/src/zmalloc.c
@@ -418,6 +418,9 @@ size_t zmalloc_get_memory_size(void) {
     if (sysctl(mib, 2, &size, &len, NULL, 0) == 0)
         return (size_t)size;
     return 0L;          /* Failed? */
+#else
+    return 0L;          /* Unknown method to get the data. */
+#endif
 #else
     return 0L;          /* Unknown OS. */
 #endif