diff --git a/lib/IRGen/IRGenDebugInfo.cpp b/lib/IRGen/IRGenDebugInfo.cpp
index 2e21338f64392..fdf8176dcce56 100644
--- a/lib/IRGen/IRGenDebugInfo.cpp
+++ b/lib/IRGen/IRGenDebugInfo.cpp
@@ -2468,6 +2468,18 @@ IRGenDebugInfoImpl::emitFunction(const SILDebugScope *DS, llvm::Function *Fn,
       /*IsLocalToUnit=*/Fn ? Fn->hasInternalLinkage() : true,
       /*IsDefinition=*/true, /*IsOptimized=*/Opts.shouldOptimize());
 
+  // When the function is a method, we only want a DW_AT_declaration there,
+  // because LLVM LTO can't unify type definitions when a child DIE is a full
+  // subprogram definition.
+  if (Rep == SILFunctionTypeRepresentation::Method) {
+    llvm::DISubprogram::DISPFlags SPFlags = llvm::DISubprogram::toSPFlags(
+        /*IsLocalToUnit=*/Fn ? Fn->hasInternalLinkage() : true,
+        /*IsDefinition=*/false, /*IsOptimized=*/Opts.shouldOptimize());
+    Decl = DBuilder.createMethod(Scope, Name, LinkageName, File, Line, DIFnTy,
+                                 0, 0, nullptr, Flags, SPFlags,
+                                 TemplateParameters, Error);
+  }
+
   // Construct the DISubprogram.
   llvm::DISubprogram *SP = DBuilder.createFunction(
       Scope, Name, LinkageName, File, Line, DIFnTy, ScopeLine, Flags, SPFlags,
diff --git a/test/DebugInfo/method-declaration.swift b/test/DebugInfo/method-declaration.swift
new file mode 100644
index 0000000000000..b1fdb35d5dfa0
--- /dev/null
+++ b/test/DebugInfo/method-declaration.swift
@@ -0,0 +1,37 @@
+// RUN: %target-swift-frontend -primary-file %s -emit-ir -gdwarf-types -o - | %FileCheck %s
+
+// Verify that we added a declaration for a method.
+
+// CHECK: define{{.*}}foo_static_method{{.*}} !dbg ![[FOO_STATIC_METHOD_DEF_DBG:[0-9]+]]
+// CHECK: define{{.*}}foo_method{{.*}} !dbg ![[FOO_METHOD_DEF_DBG:[0-9]+]]
+// CHECK: define{{.*}}bar_static_method{{.*}} !dbg ![[BAR_STATIC_METHOD_DEF_DBG:[0-9]+]]
+// CHECK: define{{.*}}bar_method{{.*}} !dbg ![[BAR_METHOD_DEF_DBG:[0-9]+]]
+// CHECK: define{{.*}}a_function{{.*}} !dbg ![[FUNC_DEF_DBG:[0-9]+]]
+
+// CHECK-DAG: ![[FOO_DBG:[0-9]+]] = !DICompositeType(tag: {{.*}} name: "Foo", {{.*}} identifier:
+public struct Foo {
+// CHECK-DAG: ![[FOO_STATIC_METHOD_DEF_DBG]] = distinct !DISubprogram(name: "foo_static_method"{{.*}}, scope: ![[FOO_DBG]]{{.*}}DISPFlagDefinition{{.*}}, declaration: ![[FOO_STATIC_METHOD_DECL_DBG:[0-9]+]]
+// CHECK-DAG: ![[FOO_STATIC_METHOD_DECL_DBG]] = !DISubprogram(name: "foo_static_method"{{.*}}, scope: ![[FOO_DBG]]
+    static func foo_static_method() {}
+// CHECK-DAG: ![[FOO_METHOD_DEF_DBG]] = distinct !DISubprogram(name: "foo_method"{{.*}}, scope: ![[FOO_DBG]]{{.*}}DISPFlagDefinition{{.*}}, declaration: ![[FOO_METHOD_DECL_DBG:[0-9]+]]
+// CHECK-DAG: ![[FOO_METHOD_DECL_DBG]] = !DISubprogram(name: "foo_method"{{.*}}, scope: ![[FOO_DBG]]
+    func foo_method() {}
+}
+
+// CHECK-DAG: ![[BAR_DBG:[0-9]+]] = !DICompositeType(tag: {{.*}} name: "Bar", {{.*}} identifier:
+public class Bar {
+// CHECK-DAG: ![[BAR_STATIC_METHOD_DEF_DBG]] = distinct !DISubprogram(name: "bar_static_method"{{.*}}, scope: ![[BAR_DBG]]{{.*}}DISPFlagDefinition{{.*}}, declaration: ![[BAR_STATIC_METHOD_DECL_DBG:[0-9]+]]
+// CHECK-DAG: ![[BAR_STATIC_METHOD_DECL_DBG]] = !DISubprogram(name: "bar_static_method"{{.*}}, scope: ![[BAR_DBG]]
+    static func bar_static_method() {}
+// CHECK-DAG: ![[BAR_METHOD_DEF_DBG]] = distinct !DISubprogram(name: "bar_method"{{.*}}, scope: ![[BAR_DBG]]{{.*}}DISPFlagDefinition{{.*}}, declaration: ![[BAR_METHOD_DECL_DBG:[0-9]+]]
+// CHECK-DAG: ![[BAR_METHOD_DECL_DBG]] = !DISubprogram(name: "bar_method"{{.*}}, scope: ![[BAR_DBG]]
+    func bar_method() {}
+}
+
+// CHECK: ![[FUNC_DEF_DBG]] = distinct !DISubprogram(name: "a_function"
+// CHECK-NOT: declaration
+// CHECK-SAME: DISPFlagDefinition
+// CHECK-NOT: declaration
+// CHECK-SAME: )
+func a_function() {}
+