diff --git a/ci/test/00_setup_env_win64.sh b/ci/test/00_setup_env_win64.sh
index 487f90e43c487f..d43a9d03798b44 100755
--- a/ci/test/00_setup_env_win64.sh
+++ b/ci/test/00_setup_env_win64.sh
@@ -15,7 +15,3 @@ export RUN_SECURITY_TESTS="false"
 export GOAL="deploy"
 export BITCOIN_CONFIG="--enable-gui --enable-reduce-exports --disable-miner --without-boost-process"
 export DIRECT_WINE_EXEC_TESTS=true
-
-# Compiler for MinGW-w64 causes false -Wreturn-type warning.
-# See https://sourceforge.net/p/mingw-w64/bugs/306/
-export NO_WERROR=1
diff --git a/configure.ac b/configure.ac
index 50441b50fb199a..b8dfee05321080 100644
--- a/configure.ac
+++ b/configure.ac
@@ -462,7 +462,13 @@ if test "x$enable_werror" = "xyes"; then
   AX_CHECK_COMPILE_FLAG([-Werror=range-loop-analysis],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=range-loop-analysis"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Werror=unused-variable],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=unused-variable"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Werror=date-time],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=date-time"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=return-type],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=return-type"],,[[$CXXFLAG_WERROR]])
+
+  dnl -Wreturn-type is broken in GCC for MinGW-w64.
+  dnl https://sourceforge.net/p/mingw-w64/bugs/306/
+  AX_CHECK_COMPILE_FLAG([-Werror=return-type], [ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=return-type"], [], [$CXXFLAG_WERROR],
+                        [AC_LANG_SOURCE([[#include <cassert>
+                                          int f(){ assert(false); }]])])
+
   AX_CHECK_COMPILE_FLAG([-Werror=conditional-uninitialized],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=conditional-uninitialized"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Werror=sign-compare],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=sign-compare"],,[[$CXXFLAG_WERROR]])
   dnl -Wsuggest-override is broken with GCC before 9.2
diff --git a/src/qt/winshutdownmonitor.h b/src/qt/winshutdownmonitor.h
index c8a523a538e0f3..02aad606c1d357 100644
--- a/src/qt/winshutdownmonitor.h
+++ b/src/qt/winshutdownmonitor.h
@@ -17,7 +17,7 @@ class WinShutdownMonitor : public QAbstractNativeEventFilter
 {
 public:
     /** Implements QAbstractNativeEventFilter interface for processing Windows messages */
-    bool nativeEventFilter(const QByteArray &eventType, void *pMessage, long *pnResult);
+    bool nativeEventFilter(const QByteArray &eventType, void *pMessage, long *pnResult) override;
 
     /** Register the reason for blocking shutdown on Windows to allow clean client exit */
     static void registerShutdownBlockReason(const QString& strReason, const HWND& mainWinId);