diff --git a/lib/AST/ASTDemangler.cpp b/lib/AST/ASTDemangler.cpp
index 846d43d126d..a62747201c3 100644
--- a/lib/AST/ASTDemangler.cpp
+++ b/lib/AST/ASTDemangler.cpp
@@ -1032,8 +1032,12 @@ ModuleDecl *
 ASTBuilder::findModule(NodePointer node) {
   assert(node->getKind() == Demangle::Node::Kind::Module);
   const auto moduleName = node->getText();
+  // Respect the main module's ABI name when we're trying to resolve
+  // mangled names. But don't touch anything under the Swift stdlib's
+  // umbrella. 
   if (Ctx.MainModule && Ctx.MainModule->getABIName().is(moduleName))
-    return Ctx.MainModule;
+    if (!Ctx.MainModule->getABIName().is(STDLIB_NAME))
+      return Ctx.MainModule;
 
   return Ctx.getModuleByName(moduleName);
 }
diff --git a/test/ModuleInterface/Inputs/opaque-type-abi-name/Bottom.swiftinterface b/test/ModuleInterface/Inputs/opaque-type-abi-name/Bottom.swiftinterface
index 33a166f7788..f6b754dff7f 100644
--- a/test/ModuleInterface/Inputs/opaque-type-abi-name/Bottom.swiftinterface
+++ b/test/ModuleInterface/Inputs/opaque-type-abi-name/Bottom.swiftinterface
@@ -3,16 +3,21 @@
 
 import Swift
 
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
 public protocol Aspect {
   associatedtype Orientation : Bottom.Aspect
   var orientation: Self.Orientation { get }
 }
 
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
 public struct Parameter {
 }
 
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
 public struct ReferencesTop {
+  @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
   public func orientation(of parameter: Bottom.Parameter) -> some Bottom.Aspect
 
+  @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
   public typealias Orientation = @_opaqueReturnTypeOf("$s3Top13ReferencesTopV11orientation2ofQrAA9ParameterV_tF", 0) __
 }
diff --git a/test/ModuleInterface/Inputs/opaque-type-abi-name/test.sh b/test/ModuleInterface/Inputs/opaque-type-abi-name/test.sh
deleted file mode 100644
index 78ae28cbdad..00000000000
--- a/test/ModuleInterface/Inputs/opaque-type-abi-name/test.sh
+++ /dev/null
@@ -1,3 +0,0 @@
-#!/bin/sh
-
-/Users/rwidmann/SwiftInternal/build/Ninja-Release/swift-macosx-arm64/bin/swift-frontend -sdk $(xcrun --show-sdk-path) -compile-module-from-interface -module-name Bottom -o Bottom.swiftmodule Bottom.swiftinterface -verify