diff --git a/configure.ac b/configure.ac
index 240d27a..7a694a2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -634,6 +634,9 @@
 ],
 [enable_debug="0"]
 )
+if test "x$enable_debug" = "x1" ; then
+  AC_DEFINE([JEMALLOC_DEBUG], [ ])
+fi
 AC_SUBST([enable_debug])
 
 dnl Only optimize if not debugging.