diff --git a/system/systrace/systrace.SlackBuild b/system/systrace/systrace.SlackBuild
index 0aa24a8c06..5ed96ae898 100644
--- a/system/systrace/systrace.SlackBuild
+++ b/system/systrace/systrace.SlackBuild
@@ -55,7 +55,7 @@ find -L . \
 
 ## First, systrace itself (backend + textmode UI):
 
-CFLAGS="$SLKCFLAGS" \
+CFLAGS="$SLKCFLAGS -std=gnu89" \
 CXXFLAGS="$SLKCFLAGS" \
 ./configure \
   --prefix=/usr \
@@ -105,7 +105,7 @@ if [ "${GUI:-yes}" = "yes" ]; then
 
   autoreconf -if
 
-  CFLAGS="$SLKCFLAGS" \
+  CFLAGS="$SLKCFLAGS -std=gnu89" \
   CXXFLAGS="$SLKCFLAGS" \
   ./configure \
     --prefix=/usr \