diff --git a/firefox.spec b/firefox.spec
index 775527c..c2050d3 100644
--- a/firefox.spec
+++ b/firefox.spec
@@ -492,7 +492,7 @@ find ./ -name config.guess -exec cp /usr/lib/rpm/config.guess {} ';'
 #
 # Disable C++ exceptions since Mozilla code is not exception-safe
 #
-MOZ_OPT_FLAGS=$(echo "$RPM_OPT_FLAGS" | %{__sed} -e 's/-Wall//')
+MOZ_OPT_FLAGS=$(echo "%{optflags}" | %{__sed} -e 's/-Wall//')
 #rhbz#1037063
 # -Werror=format-security causes build failures when -Wno-format is explicitly given
 # for some sources