diff --git a/libpkgconf/fragment.c b/libpkgconf/fragment.c
index 907a6e0..cdc9c24 100644
--- a/libpkgconf/fragment.c
+++ b/libpkgconf/fragment.c
@@ -38,6 +38,7 @@ pkgconf_fragment_is_unmergeable(const char *string)
 		{"-framework", 10},
 		{"-isystem", 8},
 		{"-idirafter", 10},
+		{"-pthread", 8}
 	};
 
 	if (*string != '-')