diff --git a/var/spack/repos/builtin/packages/fmt/package.py b/var/spack/repos/builtin/packages/fmt/package.py
index 18bc8518cb6..3464c3c4d01 100644
--- a/var/spack/repos/builtin/packages/fmt/package.py
+++ b/var/spack/repos/builtin/packages/fmt/package.py
@@ -37,7 +37,7 @@ def cmake_args(self):
         spec = self.spec
         args = []
         if '+pic' in spec:
-            args.append([
+            args.extend([
                 '-DCMAKE_C_FLAGS={0}'.format(self.compiler.pic_flag),
                 '-DCMAKE_CXX_FLAGS={0}'.format(self.compiler.pic_flag)
             ])