diff --git a/cinelerra-5.1/configure.ac b/cinelerra-5.1/configure.ac
index f61ef27..ae9aefd 100644
--- a/cinelerra-5.1/configure.ac
+++ b/cinelerra-5.1/configure.ac
@@ -8,6 +8,46 @@ AC_LANG_CPLUSPLUS
 AC_LANG_C
 AC_PROG_CXX
 
+dnl Enable and choose c++ standard
+AC_ARG_ENABLE(cxxstd,
+              AC_HELP_STRING([--enable-cxxstd=14],
+                             [enable ISO c++ standard 11/14 [[default=auto]]]),
+              [cxxstd="${enableval}"], [cxxstd=14])
+
+if test "${cxxstd}" = 17 ; then
+    AX_CXX_COMPILE_STDCXX([17], [noext], [mandatory])
+	CXXFLAGS="$CXXFLAGS -std=c++17"
+else
+  if test "${cxxstd}" = 14 ; then
+      AX_CXX_COMPILE_STDCXX([14], [noext], [mandatory])
+	CXXFLAGS="$CXXFLAGS -std=c++14"
+  else
+    if test "${cxxstd}" = 11 ; then
+      AX_CXX_COMPILE_STDCXX([11], [noext], [mandatory])
+      CXXFLAGS="$CXXFLAGS -std=c++11"
+    else
+      if test "${cxxstd}" = 03 ; then
+        CXXFLAGS="$CXXFLAGS -std=c++03"
+      else
+        dnl automatically determine...
+        AX_CXX_COMPILE_STDCXX([11], [noext], [optional])
+        AX_CXX_COMPILE_STDCXX([14], [noext], [optional])
+        AX_CXX_COMPILE_STDCXX([17], [noext], [optional])
+        if test "$HAVE_CXX14" = 1 ; then
+	 CXXFLAGS="$CXXFLAGS -std=c++14"
+          cxxstd = 14
+        else
+          if test "$HAVE_CXX11" = 1 ; then
+	 CXXFLAGS="$CXXFLAGS -std=c++11"
+            cxxstd = 11
+          fi
+        fi
+      fi
+    fi
+  fi
+fi
+
+CFG_CFLAGS+= $CXXFLAGS
 CFG_CFLAGS+=" -fno-omit-frame-pointer -fno-math-errno -fno-signed-zeros"
 CFG_CFLAGS+=" -pthread -Wall"
 # misguided pedantic warnings