2 files changed, 24 insertions, 0 deletions
diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 66c2f9796..f4c8cd847 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -4065,6 +4065,13 @@ Expr* SemanticsExprVisitor::visitIsTypeExpr(IsTypeExpr* expr)
     expr->type = m_astBuilder->getBoolType();
     expr->value = originalVal;
 
+    // Check if the right-hand side type is an interface type
+    if (isInterfaceType(expr->typeExpr.type))
+    {
+        getSink()->diagnose(expr, Diagnostics::isAsOperatorCannotUseInterfaceAsRHS);
+        return expr;
+    }
+
     auto valueType = expr->value->type.type;
     if (auto typeType = as<TypeType>(valueType))
         valueType = typeType->getType();
@@ -4103,6 +4110,15 @@ Expr* SemanticsExprVisitor::visitAsTypeExpr(AsTypeExpr* expr)
     TypeExp typeExpr;
     typeExpr.exp = expr->typeExpr;
     typeExpr = CheckProperType(typeExpr);
+
+    // Check if the right-hand side type is an interface type
+    if (isInterfaceType(typeExpr.type))
+    {
+        getSink()->diagnose(expr, Diagnostics::isAsOperatorCannotUseInterfaceAsRHS);
+        expr->type = m_astBuilder->getErrorType();
+        return expr;
+    }
+
     expr->value = CheckTerm(expr->value);
     auto optType = m_astBuilder->getOptionalType(typeExpr.type);
     expr->type = optType;
diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index bef32e20e..f4741ab04 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -842,7 +842,15 @@ DIAGNOSTIC(
     isOperatorValueMustBeInterfaceType,
     "'is'/'as' operator requires an interface-typed expression.")
 
+DIAGNOSTIC(
+    30301,
+    Error,
+    isAsOperatorCannotUseInterfaceAsRHS,
+    "'is' and 'as' operators do not support interface types as the right-hand side. Use a concrete "
+    "type instead.")
+
 DIAGNOSTIC(33070, Error, expectedFunction, "expected a function, got '$0'")
+
 DIAGNOSTIC(33071, Error, expectedAStringLiteral, "expected a string literal")
 
 // `dyn` and `some` errors