diff --git a/src/r_things.c b/src/r_things.c
index 7d9701105..076777597 100644
--- a/src/r_things.c
+++ b/src/r_things.c
@@ -433,6 +433,9 @@ boolean R_AddSingleSpriteDef(const char *sprname, spritedef_t *spritedef, UINT16
 
 	for (l = startlump; l < endlump; l++)
 	{
+		if (W_IsLumpFolder(wadnum, l))
+			I_Error("R_AddSingleSpriteDef: all frame lumps for a sprite should be contained inside a single folder\n");
+
 		// For long sprites, the startlump-endlump range only includes
 		// relevant lumps, so no check needed in that case
 		if (longname || (strlen(sprname) == 4 && !memcmp(lumpinfo[l].name, sprname, 4)))