diff --git a/var/spack/repos/builtin/packages/dealii/package.py b/var/spack/repos/builtin/packages/dealii/package.py
index 186d17db1e7..222691c69ec 100644
--- a/var/spack/repos/builtin/packages/dealii/package.py
+++ b/var/spack/repos/builtin/packages/dealii/package.py
@@ -602,6 +602,11 @@ def cmake_args(self):
             options.extend(
                 [
                     self.define("CMAKE_CXX_FLAGS_RELEASE", " ".join(cxx_flags_release)),
+                ]
+            )
+        if len(cxx_flags) > 0:
+            options.extend(
+                [
                     self.define("CMAKE_CXX_FLAGS", " ".join(cxx_flags)),
                 ]
             )