diff --git a/dlls/d3dx9_36/preshader.c b/dlls/d3dx9_36/preshader.c
index fbd99ac58f9..bd934af4b5a 100644
--- a/dlls/d3dx9_36/preshader.c
+++ b/dlls/d3dx9_36/preshader.c
@@ -104,7 +104,11 @@ static double pres_log(double *args, int n)
     if (v == 0.0)
         return 0.0;
     else
+#ifdef HAVE_LOG2
         return log2(v);
+#else
+        return log(v) / log(2);
+#endif
 }
 
 #define PRES_OPCODE_MASK 0x7ff00000