diff --git a/src/r_data/models/models.cpp b/src/r_data/models/models.cpp
index ad4e72576..ce41e064d 100644
--- a/src/r_data/models/models.cpp
+++ b/src/r_data/models/models.cpp
@@ -415,7 +415,7 @@ static unsigned FindModel(const char * path, const char * modelfile)
 	FMemLump lumpd = Wads.ReadLump(lump);
 	char * buffer = (char*)lumpd.GetMem();
 
-	if ( fullname.IndexOf("_d.3d") == fullname.Len()-5 )
+	if ( (size_t)fullname.IndexOf("_d.3d") == fullname.Len()-5 )
 	{
 		FString anivfile = fullname.GetChars();
 		anivfile.Substitute("_d.3d","_a.3d");
@@ -424,7 +424,7 @@ static unsigned FindModel(const char * path, const char * modelfile)
 			model = new FUE1Model;
 		}
 	}
-	else if ( fullname.IndexOf("_a.3d") == fullname.Len()-5 )
+	else if ( (size_t)fullname.IndexOf("_a.3d") == fullname.Len()-5 )
 	{
 		FString datafile = fullname.GetChars();
 		datafile.Substitute("_a.3d","_d.3d");
diff --git a/src/r_data/models/models_ue1.cpp b/src/r_data/models/models_ue1.cpp
index e07f471b9..d7394bd79 100644
--- a/src/r_data/models/models_ue1.cpp
+++ b/src/r_data/models/models_ue1.cpp
@@ -46,7 +46,7 @@ bool FUE1Model::Load( const char *filename, int lumpnum, const char *buffer, int
 	FMemLump lump2;
 	const char *buffer2;
 	FString realfilename = Wads.GetLumpFullName(lumpnum);
-	if ( realfilename.IndexOf("_d.3d") == realfilename.Len()-5 )
+	if ( (size_t)realfilename.IndexOf("_d.3d") == realfilename.Len()-5 )
 	{
 		realfilename.Substitute("_d.3d","_a.3d");
 		lumpnum2 = Wads.CheckNumForFullName(realfilename);