diff --git a/code/ryzom/tools/patch_gen/patch_gen_common.cpp b/code/ryzom/tools/patch_gen/patch_gen_common.cpp
index c1290cfd5..be9433279 100644
--- a/code/ryzom/tools/patch_gen/patch_gen_common.cpp
+++ b/code/ryzom/tools/patch_gen/patch_gen_common.cpp
@@ -55,8 +55,10 @@ void GeneratePatch(const std::string& srcFileName,const std::string& destFileNam
 #ifdef NL_OS_WINDOWS
 	_spawnlp(_P_WAIT, "xdelta.exe","xdelta.exe","delta",srcFileName.c_str(),destFileName.c_str(),patchFileName.c_str(),NULL);
 #else // NL_OS_WINDOWS
+	// xdelta-1.x behaves like "diff" and returns 0 for identical files, 1 for different files, 2 for errors
 	sint error = system (cmd.c_str());
-	if (error)
+
+	if (error == 2)
 		nlwarning("'%s' failed with error code %d", cmd.c_str(), error);
 #endif // NL_OS_WINDOWS
 }
@@ -69,8 +71,10 @@ void ApplyPatch(const std::string& srcFileName,const std::string& destFileName,c
 #ifdef NL_OS_WINDOWS
 	_spawnlp(_P_WAIT, "xdelta.exe","xdelta.exe","patch",patchFileName.c_str(),srcFileName.c_str(),destFileName.c_str(),NULL);
 #else // NL_OS_WINDOWS
+	// xdelta-1.x behaves like "diff" and returns 0 for identical files, 1 for different files, 2 for errors
 	sint error = system (cmd.c_str());
-	if (error)
+
+	if (error == 2)
 		nlwarning("'%s' failed with error code %d", cmd.c_str(), error);
 #endif // NL_OS_WINDOWS
 }