diff --git a/serd.spec b/serd.spec
index c922949..363486a 100644
--- a/serd.spec
+++ b/serd.spec
@@ -64,7 +64,7 @@ Development files for libserd.
 for i in `grep -rl "%{_bindir}/env python"`;do sed -i '1s/^#!.*/#!\/usr\/bin\/python3/' ${i} ;done
 
 %build
-export CFLAGS='%{optflags} --std=gnu99'
+export CFLAGS='%{optflags} -std=gnu99'
 export CXXFLAGS='%{optflags}'
 ./waf configure \
   --prefix=%{_prefix} \