diff --git a/libmirage.spec b/libmirage.spec
index c4ae749..8426850 100644
--- a/libmirage.spec
+++ b/libmirage.spec
@@ -126,7 +126,7 @@ This package provides the GObject Introspection bindings for libmirage.
 
 %build
 cmake . -DCMAKE_INSTALL_PREFIX:PATH="%_prefix" \
-	-DCMAKE_C_FLAGS="%optflags" ;
+	-DCMAKE_C_FLAGS:STRING="%optflags" ;
 make %{?_smp_mflags};
 
 %install