--- a/media/webrtc/signaling/test/FakeLogging.h
+++ b/media/webrtc/signaling/test/FakeLogging.h
@@ -4,13 +4,23 @@
 
 #ifndef FakeLogging_h
 #define FakeLogging_h
 
 namespace mozilla {
 namespace detail {
 void log_print(const PRLogModuleInfo* aModule,
                       LogLevel aLevel,
-                      const char* aFmt, ...) { }
+                      const char* aFmt, ...)
+  {
+    // copied from Logging.cpp:#48-53
+    va_list ap;
+    va_start(ap, aFmt);
+    char* buff = PR_vsmprintf(aFmt, ap);
+    PR_LogPrint("%s", buff);
+    PR_smprintf_free(buff);
+    va_end(ap);
+  }
+
 }
 }
 
 #endif