1 files changed, 16 insertions, 4 deletions
diff --git a/source/slang/slang-ir-lower-generic-function.cpp b/source/slang/slang-ir-lower-generic-function.cpp
index f2b1d1a6a..c003d6125 100644
--- a/source/slang/slang-ir-lower-generic-function.cpp
+++ b/source/slang/slang-ir-lower-generic-function.cpp
@@ -296,8 +296,11 @@ struct GenericFunctionLoweringContext
     // and emission of wrapper functions.
     void lowerWitnessTable(IRWitnessTable* witnessTable)
     {
-        auto interfaceType =
-            maybeLowerInterfaceType(cast<IRInterfaceType>(witnessTable->getConformanceType()));
+        IRInterfaceType* conformanceType = as<IRInterfaceType>(witnessTable->getConformanceType());
+        if (!conformanceType)
+            return;
+
+        auto interfaceType = maybeLowerInterfaceType(conformanceType);
         IRBuilder builderStorage(sharedContext->module);
         auto builder = &builderStorage;
         builder->setInsertBefore(witnessTable);
@@ -353,8 +356,17 @@ struct GenericFunctionLoweringContext
             return;
         if (witnessTableType->getConformanceType()->findDecoration<IRComInterfaceDecoration>())
             return;
-        auto interfaceType =
-            maybeLowerInterfaceType(cast<IRInterfaceType>(witnessTableType->getConformanceType()));
+
+        IRInterfaceType* conformanceType =
+            as<IRInterfaceType>(witnessTableType->getConformanceType());
+
+        // NoneWitness generates conformance types which aren't interfaces. In
+        // that case, the method can just be skipped entirely, since there's no
+        // real witness for it and it should be in unreachable code at this
+        // point.
+        if (!conformanceType)
+            return;
+        auto interfaceType = maybeLowerInterfaceType(conformanceType);
         interfaceRequirementVal = sharedContext->findInterfaceRequirementVal(
             interfaceType,
             lookupInst->getRequirementKey());