diff --git a/src/g5dec.inl b/src/g5dec.inl
index 07ebd52..76254b4 100644
--- a/src/g5dec.inl
+++ b/src/g5dec.inl
@@ -138,11 +138,19 @@ static void Decode_Begin(G5DECIMAGE *pPage)
     pPage->ulBits = TIFFMOTOLONG(pPage->pSrc); // load 32 bits to start
     pPage->ulBitOff = 0;
     // Calculate the number of bits needed for a long horizontal code
+#ifdef __GNUC__
 #ifdef __AVR__
     pPage->iHLen = 16 - __builtin_clz(pPage->iWidth);
 #else
     pPage->iHLen = 32 - __builtin_clz(pPage->iWidth);
 #endif
+#else
+#ifdef _MSC_VER
+    pPage->iHLen = 32 - __lzcnt(pPage->iWidth);
+#else
+    #error "Unsupported compiler for G5 decoder"
+#endif // _MSC_VER
+#endif
 } /* Decode_Begin() */
 //
 // Decode a single line of G5 data (private function)