diff --git a/configure.ac b/configure.ac
--- a/configure.ac
+++ b/configure.ac
@@ -767,12 +767,17 @@
   AX_CHECK_COMPILE_FLAG([-Wstack-protector],[HARDENED_CXXFLAGS="$HARDENED_CXXFLAGS -Wstack-protector"])
   AX_CHECK_COMPILE_FLAG([-fstack-protector-all],[HARDENED_CXXFLAGS="$HARDENED_CXXFLAGS -fstack-protector-all"])
 
-  AX_CHECK_PREPROC_FLAG([-D_FORTIFY_SOURCE=2],[
-    AX_CHECK_PREPROC_FLAG([-U_FORTIFY_SOURCE],[
-      HARDENED_CPPFLAGS="$HARDENED_CPPFLAGS -U_FORTIFY_SOURCE"
+  # When enable_debug is yes, all optimizations are disabled.
+  # However, FORTIFY_SOURCE requires that there is some level of optimization, otherwise it does nothing and just creates a compiler warning.
+  # Since FORTIFY_SOURCE is a no-op without optimizations, do not enable it when enable_debug is yes.
+  if test x$enable_debug != xyes; then
+    AX_CHECK_PREPROC_FLAG([-D_FORTIFY_SOURCE=2],[
+      AX_CHECK_PREPROC_FLAG([-U_FORTIFY_SOURCE],[
+        HARDENED_CPPFLAGS="$HARDENED_CPPFLAGS -U_FORTIFY_SOURCE"
+      ])
+      HARDENED_CPPFLAGS="$HARDENED_CPPFLAGS -D_FORTIFY_SOURCE=2"
     ])
-    HARDENED_CPPFLAGS="$HARDENED_CPPFLAGS -D_FORTIFY_SOURCE=2"
-  ])
+  fi
 
   AX_CHECK_LINK_FLAG([[-Wl,--dynamicbase]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,--dynamicbase"])
   AX_CHECK_LINK_FLAG([[-Wl,--nxcompat]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,--nxcompat"])