diff --git a/mozilla/string/macbuild/String.Prefix b/mozilla/string/macbuild/String.Prefix
index e67ea4f95f9..192e8d20119 100644
--- a/mozilla/string/macbuild/String.Prefix
+++ b/mozilla/string/macbuild/String.Prefix
@@ -25,3 +25,6 @@
  */
 
 #include "MacPrefix.h"
+
+  // while we're still a part of xpcom, make stuff get exported
+#define _IMPL_NS_COM 1
diff --git a/mozilla/string/macbuild/StringDebug.Prefix b/mozilla/string/macbuild/StringDebug.Prefix
index 7696b516a8e..b196c8aae93 100644
--- a/mozilla/string/macbuild/StringDebug.Prefix
+++ b/mozilla/string/macbuild/StringDebug.Prefix
@@ -25,3 +25,6 @@
  */
 
 #include "MacPrefix_debug.h"
+
+  // while we're still a part of xpcom, make stuff get exported
+#define _IMPL_NS_COM 1
diff --git a/mozilla/xpcom/string/macbuild/String.Prefix b/mozilla/xpcom/string/macbuild/String.Prefix
index e67ea4f95f9..192e8d20119 100644
--- a/mozilla/xpcom/string/macbuild/String.Prefix
+++ b/mozilla/xpcom/string/macbuild/String.Prefix
@@ -25,3 +25,6 @@
  */
 
 #include "MacPrefix.h"
+
+  // while we're still a part of xpcom, make stuff get exported
+#define _IMPL_NS_COM 1
diff --git a/mozilla/xpcom/string/macbuild/StringDebug.Prefix b/mozilla/xpcom/string/macbuild/StringDebug.Prefix
index 7696b516a8e..b196c8aae93 100644
--- a/mozilla/xpcom/string/macbuild/StringDebug.Prefix
+++ b/mozilla/xpcom/string/macbuild/StringDebug.Prefix
@@ -25,3 +25,6 @@
  */
 
 #include "MacPrefix_debug.h"
+
+  // while we're still a part of xpcom, make stuff get exported
+#define _IMPL_NS_COM 1