diff --git a/configure.ac b/configure.ac
index 23a33b8c4f..dca4c5edd8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -427,6 +427,7 @@ if test "x$enable_werror" = "xyes"; then
   AX_CHECK_COMPILE_FLAG([-Werror=suggest-override],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=suggest-override"],,[[$CXXFLAG_WERROR]],
                         [AC_LANG_SOURCE([[struct A { virtual void f(); }; struct B : A { void f() final; };]])])
   AX_CHECK_COMPILE_FLAG([-Werror=unreachable-code-loop-increment],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=unreachable-code-loop-increment"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Werror=mismatched-tags], [ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=mismatched-tags"], [], [$CXXFLAG_WERROR])
 fi
 
 if test "x$CXXFLAGS_overridden" = "xno"; then
diff --git a/src/validation.h b/src/validation.h
index e86b3d3af8..fc7add85b7 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -40,7 +40,7 @@ class CBlockIndex;
 class CBlockTreeDB;
 class CBlockUndo;
 class CChainParams;
-class CCheckpointData;
+struct CCheckpointData;
 class CInv;
 class CConnman;
 class CScriptCheck;