--- a/gfx/gl/GLContextProviderWGL.cpp
+++ b/gfx/gl/GLContextProviderWGL.cpp
@@ -103,17 +103,17 @@ WGLLibrary::EnsureInitialized()
 
     std::string libGLFilename = "Opengl32.dll";
     // SU_SPIES_DIRECTORY is for AMD CodeXL/gDEBugger
     if (PR_GetEnv("SU_SPIES_DIRECTORY")) {
         libGLFilename = std::string(PR_GetEnv("SU_SPIES_DIRECTORY")) + "\\opengl32.dll";
     }
 
     if (!mOGLLibrary) {
-        mOGLLibrary = PR_LoadLibrary(&libGLFilename[0]);
+        mOGLLibrary = PR_LoadLibrary(libGLFilename.c_str());
         if (!mOGLLibrary) {
             NS_WARNING("Couldn't load OpenGL library.");
             return false;
         }
     }
 
     GLLibraryLoader::SymLoadStruct earlySymbols[] = {
         { (PRFuncPtr*) &fCreateContext, { "wglCreateContext", nullptr } },