diff --git a/src/MemoryX.h b/src/MemoryX.h
index 56e99171a..7c1da431c 100644
--- a/src/MemoryX.h
+++ b/src/MemoryX.h
@@ -11,7 +11,11 @@
 // std:: containers knowing about rvalue references
 #undef __AUDACITY_OLD_STD__
 
-#if defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && __MAC_OS_X_VERSION_MIN_REQUIRED <= __MAC_10_6
+
+// Clang 5.0 on OSX 10.6 CAN handle C++11, if built with -std=c++11
+// So use "< __MAC_10_6" rather than "<= __MAC_10_6"
+// Requested by macports.org https://trac.macports.org/ticket/56114
+#if defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && __MAC_OS_X_VERSION_MIN_REQUIRED < __MAC_10_6
 
 #define __AUDACITY_OLD_STD__