--- src/lib/MSWrite.cpp
+++ src/lib/MSWrite.cpp
@@ -1421,7 +1421,7 @@
 		break;
 	}
 
-	unsigned offset = MSWriteParserInternal::BM_FILE_STRUCT_SIZE + MSWriteParserInternal::BM_INFO_V2_STRUCT_SIZE + colors * unsigned(sizeof(MSWriteParserInternal::BitmapPalette));
+	unsigned offset = +MSWriteParserInternal::BM_FILE_STRUCT_SIZE + MSWriteParserInternal::BM_INFO_V2_STRUCT_SIZE + colors * unsigned(sizeof(MSWriteParserInternal::BitmapPalette));
 
 	// File header
 	bmpdata.append('B');
@@ -1513,7 +1513,7 @@
 	bmpdata.append('M');
 	MSWriteParserInternal::appendU32(bmpdata, size + MSWriteParserInternal::BM_FILE_STRUCT_SIZE);
 	MSWriteParserInternal::appendU32(bmpdata, 0);
-	MSWriteParserInternal::appendU32(bmpdata, MSWriteParserInternal::BM_FILE_STRUCT_SIZE + MSWriteParserInternal::BM_INFO_V3_STRUCT_SIZE + 4 * colors);
+	MSWriteParserInternal::appendU32(bmpdata, +MSWriteParserInternal::BM_FILE_STRUCT_SIZE + MSWriteParserInternal::BM_INFO_V3_STRUCT_SIZE + 4 * colors);
 
 	bmpdata.append(data, size);