diff --git a/src/compatibility.cpp b/src/compatibility.cpp
index cbbe12f73e..4a4f19d6be 100644
--- a/src/compatibility.cpp
+++ b/src/compatibility.cpp
@@ -90,6 +90,7 @@ enum
 // PRIVATE FUNCTION PROTOTYPES ---------------------------------------------
 
 // EXTERNAL DATA DECLARATIONS ----------------------------------------------
+extern TArray<FMapThing> MapThingsConverted;
 
 // PUBLIC DATA DEFINITIONS -------------------------------------------------
 
@@ -510,7 +511,7 @@ void SetCompatibilityParams()
 				case CP_SETTHINGZ:
 				{
 					// When this is called, the things haven't been spawned yet so we can alter the position inside the MapThings array.
-					if (CompatParams[i+1] < MapThingsConverted.Size())
+					if ((unsigned)CompatParams[i+1] < MapThingsConverted.Size())
 					{
 						MapThingsConverted[CompatParams[i+1]].z = CompatParams[i+2];
 					}
diff --git a/wadsrc/static/compatibility.txt b/wadsrc/static/compatibility.txt
index 209ae2aa2e..a84ba218b7 100644
--- a/wadsrc/static/compatibility.txt
+++ b/wadsrc/static/compatibility.txt
@@ -347,3 +347,9 @@ F481922F4881F74760F3C0437FD5EDD0 // map03
 	setlinespecial 397 NoiseAlert 0 0 0 0 0
 	setlinespecial 411 NoiseAlert 0 0 0 0 0
 }
+
+952CC8D03572E17BA550B01B366EFBB9 // Cheogsh map01
+{
+	// make the blue key spawn above the 3D floor
+	setthingz 918 296
+}