diff --git a/code/nel/tools/3d/build_interface/main.cpp b/code/nel/tools/3d/build_interface/main.cpp
index 04213d34b..c56934662 100644
--- a/code/nel/tools/3d/build_interface/main.cpp
+++ b/code/nel/tools/3d/build_interface/main.cpp
@@ -263,10 +263,12 @@ int main(int argc, char **argv)
 			pBtmp = new NLMISC::CBitmap;
 			NLMISC::CIFile inFile;
 
-			if (!inFile.open(AllMapNames[i])) throw NLMISC::Exception("Unable to open " + AllMapNames[i]);
+			if (!inFile.open(AllMapNames[i])) throw NLMISC::Exception(toString("Unable to open %s", AllMapNames[i].c_str()));
 
 			uint8 colors = pBtmp->load(inFile);
 
+			if (!colors) throw NLMISC::Exception(toString("%s is not a bitmap", AllMapNames[i].c_str()));
+
 			if (pBtmp->getPixelFormat() != CBitmap::RGBA)
 			{
 				outString(toString("Converting %s to RGBA (32 bits), originally using %u bits...", AllMapNames[i].c_str(), (uint)colors));