diff --git a/lib/isc/mem.c b/lib/isc/mem.c
index d9018f6dbe..2abb91c7a2 100644
--- a/lib/isc/mem.c
+++ b/lib/isc/mem.c
@@ -46,8 +46,10 @@
 /* On DragonFly BSD the header does not provide jemalloc API */
 #if defined(HAVE_MALLOC_NP_H) && !defined(__DragonFly__)
 #include <malloc_np.h>
+#define JEMALLOC_API_SUPPORTED 1
 #elif defined(HAVE_JEMALLOC)
 #include <jemalloc/jemalloc.h>
+#define JEMALLOC_API_SUPPORTED 1
 
 #if JEMALLOC_VERSION_MAJOR < 4
 #define sdallocx(ptr, size, flags) dallocx(ptr, flags)