diff --git a/src/lib/sw_engine/tvgSwRle.cpp b/src/lib/sw_engine/tvgSwRle.cpp
index 25b9c03a..1d3d4987 100644
--- a/src/lib/sw_engine/tvgSwRle.cpp
+++ b/src/lib/sw_engine/tvgSwRle.cpp
@@ -145,9 +145,9 @@ static void _genSpan(SwRleData* rle, SwSpan* spans, size_t count)
     /* alloc is required to prevent free and reallocation */
     /* when the rle needs to be regenerated because of attribute change. */
     if (rle->alloc < newSize) {
-        rle->spans = static_cast<SwSpan*>(realloc(rle->spans, newSize * sizeof(SwSpan)));
+        rle->spans = static_cast<SwSpan*>(realloc(rle->spans, (count + rle->size) << 2 * sizeof(SwSpan)));
         assert(rle->spans);
-        rle->alloc = newSize;
+        rle->alloc = rle->size + (count << 2);
     }
 
     //copy the new spans to the allocated memory