diff --git a/firefox.spec b/firefox.spec
index 6e6b4f1..4f8105d 100644
--- a/firefox.spec
+++ b/firefox.spec
@@ -473,6 +473,10 @@ MOZ_OPT_FLAGS=$(echo "$MOZ_OPT_FLAGS" | %{__sed} -e 's/-O2//')
 %endif
 %ifarch s390
 MOZ_OPT_FLAGS=$(echo "$MOZ_OPT_FLAGS" | %{__sed} -e 's/-g/-g1/')
+# If MOZ_DEBUG_FLAGS is empty, firefox's build will default it to "-g" which
+# overrides the -g1 from line above and breaks building on s390
+# (OOM when linking, rhbz#1238225)
+export MOZ_DEBUG_FLAGS=" "
 %endif
 %ifarch s390 %{arm} ppc aarch64
 MOZ_LINK_FLAGS="-Wl,--no-keep-memory -Wl,--reduce-memory-overheads"