diff --git a/src/bimg_p.h b/src/bimg_p.h
index ff968d8..52e759b 100644
--- a/src/bimg_p.h
+++ b/src/bimg_p.h
@@ -85,7 +85,7 @@ namespace bimg
 		if (_hasMips)
 		{
 			const uint32_t max = bx::max(_width, _height, _depth);
-			const uint32_t num = 1 + bx::ceilLog2(max);
+			const uint32_t num = 1 + bx::floorLog2(max);
 
 			return uint8_t(num);
 		}