diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2ff6e1eab..1540d87ec 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -45,7 +45,7 @@ jobs:
             python: '3.6'
             args: >
               -DPYBIND11_FINDPYTHON=ON
-# BREAKS      -DCMAKE_CXX_FLAGS="-D_=1"
+              -DCMAKE_CXX_FLAGS="-D_=1"
           - runs-on: windows-latest
             python: '3.6'
             args: >
diff --git a/.github/workflows/ci_sh_def.yml b/.github/workflows/ci_sh_def.yml
index f9c3d6594..aa01aa035 100644
--- a/.github/workflows/ci_sh_def.yml
+++ b/.github/workflows/ci_sh_def.yml
@@ -57,7 +57,7 @@ jobs:
             python: '3.6'
             args: >
               -DPYBIND11_FINDPYTHON=ON
-# BREAKS      -DCMAKE_CXX_FLAGS="-D_=1"
+              -DCMAKE_CXX_FLAGS="-D_=1"
           - runs-on: windows-latest
             python: '3.6'
             args: >
diff --git a/tests/pure_cpp/smart_holder_poc_test.cpp b/tests/pure_cpp/smart_holder_poc_test.cpp
index e414930a8..cbdbc25f2 100644
--- a/tests/pure_cpp/smart_holder_poc_test.cpp
+++ b/tests/pure_cpp/smart_holder_poc_test.cpp
@@ -1,5 +1,10 @@
 #include "pybind11/detail/smart_holder_poc.h"
 
+// Catch uses _ internally, which breaks gettext style defines
+#ifdef _
+#    undef _
+#endif
+
 #define CATCH_CONFIG_MAIN
 #include "catch.hpp"