diff --git a/lib/ClangImporter/SwiftDeclSynthesizer.cpp b/lib/ClangImporter/SwiftDeclSynthesizer.cpp
index 617aee360edf4..d1c8535d7e9a3 100644
--- a/lib/ClangImporter/SwiftDeclSynthesizer.cpp
+++ b/lib/ClangImporter/SwiftDeclSynthesizer.cpp
@@ -21,6 +21,7 @@
 #include "swift/AST/ParameterList.h"
 #include "swift/AST/Pattern.h"
 #include "swift/AST/Stmt.h"
+#include "swift/AST/TypeCheckRequests.h"
 #include "swift/Basic/Assertions.h"
 #include "clang/AST/Mangle.h"
 #include "clang/Sema/DelayedDiagnostic.h"
@@ -2532,6 +2533,11 @@ SwiftDeclSynthesizer::makeDefaultArgument(const clang::ParmVarDecl *param,
   funcDecl->setAccess(AccessLevel::Public);
   funcDecl->getAttrs().add(new (ctx)
                                AlwaysEmitIntoClientAttr(/*IsImplicit=*/true));
+  // At this point, the parameter/return types of funcDecl might not be imported
+  // into Swift completely, meaning that their protocol conformances might not
+  // be populated yet. Prevent LifetimeDependenceInfoRequest from prematurely
+  // populating the conformance table for the types involved.
+  ctx.evaluator.cacheOutput(LifetimeDependenceInfoRequest{funcDecl}, {});
 
   ImporterImpl.defaultArgGenerators[param] = funcDecl;