diff --git a/core/src/main/kotlin/org/vorpal/research/kex/util/kfg.kt b/core/src/main/kotlin/org/vorpal/research/kex/util/kfg.kt
index 438776f80..443e28850 100644
--- a/core/src/main/kotlin/org/vorpal/research/kex/util/kfg.kt
+++ b/core/src/main/kotlin/org/vorpal/research/kex/util/kfg.kt
@@ -146,10 +146,10 @@ fun Class.getCtor(vararg argTypes: Type) =
     getMethod("<init>", cm.type.voidType, *argTypes)
 
 private object SubTypeInfoCache {
-    private val subtypeCache = mutableMapOf<Pair<Type, Type>, Boolean>()
-    fun check(lhv: Type, rhv: Type): Boolean = subtypeCache.getOrPut(lhv to rhv) {
+    private val subtypeCache = mutableMapOf<Pair<String, String>, Boolean>()
+    fun check(lhv: Type, rhv: Type): Boolean = subtypeCache.getOrPut(lhv.toString() to rhv.toString()) {
         lhv.isSubtypeOf(rhv)
     }
 }
 
-fun Type.isSubtypeOfCached(other: Type): Boolean = SubTypeInfoCache.check(this, other)
+fun Type.isSubtypeOfCached(other: Type): Boolean = this.isSubtypeOf(other)
diff --git a/kex.py b/kex.py
index 55bdde1e1..08666edf3 100755
--- a/kex.py
+++ b/kex.py
@@ -60,4 +60,4 @@ def main() -> int:
 
 if __name__ == "__main__":
 	returnCode = main()
-	sys.exit(returnCode)
\ No newline at end of file
+	sys.exit(returnCode)