diff --git a/lib/IRGen/IRGenSIL.cpp b/lib/IRGen/IRGenSIL.cpp
index 8745f1961dddf..2a1e37df82ada 100644
--- a/lib/IRGen/IRGenSIL.cpp
+++ b/lib/IRGen/IRGenSIL.cpp
@@ -4040,8 +4040,9 @@ void IRGenSILFunction::visitFullApplySite(FullApplySite site) {
       Builder.emitBlock(typedErrorLoadBB);
 
       auto &errorTI = cast<LoadableTypeInfo>(IGM.getTypeInfo(errorType));
-      auto silResultTy = CurSILFn->mapTypeIntoContext(
-          substConv.getSILResultType(IGM.getMaximalTypeExpansionContext()));
+      auto silResultTy =
+          substConv.getSILResultType(IGM.getMaximalTypeExpansionContext());
+      ASSERT(!silResultTy.hasTypeParameter());
       auto &resultTI = cast<LoadableTypeInfo>(IGM.getTypeInfo(silResultTy));
 
       auto &resultSchema = resultTI.nativeReturnValueSchema(IGM);
diff --git a/test/IRGen/typed_throws_generic.swift b/test/IRGen/typed_throws_generic.swift
new file mode 100644
index 0000000000000..95794512cedc9
--- /dev/null
+++ b/test/IRGen/typed_throws_generic.swift
@@ -0,0 +1,20 @@
+// RUN: %target-swift-frontend -primary-file %s -emit-irgen
+
+// https://github.com/swiftlang/swift/issues/80020
+//
+// We used to assert if you had a loadable return type that contained
+// a generic parameter.
+
+public enum MyError: Error {
+  case error
+}
+
+public struct G<T> {}  // Note: G<T> is loadable
+
+public func f<T>(t: T) throws(MyError) -> G<T> {
+  return G<T>()
+}
+
+public func g<U>(u: U?) throws(MyError) -> G<U?> {
+  return try f(t: u)
+}
\ No newline at end of file