diff --git a/lib/isc/include/isc/mem.h b/lib/isc/include/isc/mem.h
index 3201ba4c8b..ab8dd2c2c0 100644
--- a/lib/isc/include/isc/mem.h
+++ b/lib/isc/include/isc/mem.h
@@ -190,7 +190,13 @@ extern unsigned int isc_mem_defaultflags;
  * for more information.
  */
 #if HAVE_JEMALLOC
-#include <jemalloc/jemalloc.h>
+
+/*
+ * cmocka.h has confliction definitions with the jemalloc header but we only
+ * need the mallocx symbol from jemalloc.
+ */
+void *
+mallocx(size_t size, int flags);
 
 extern volatile void *isc__mem_malloc;