diff --git a/lib/AST/Mangle.cpp b/lib/AST/Mangle.cpp
index ed0aecc95ae24..270c26f0c2c58 100644
--- a/lib/AST/Mangle.cpp
+++ b/lib/AST/Mangle.cpp
@@ -1590,7 +1590,7 @@ void Mangler::mangleEntity(const ValueDecl *decl,
                            unsigned uncurryLevel) {
   assert(!isa<ConstructorDecl>(decl));
   assert(!isa<DestructorDecl>(decl));
-  
+
   // entity ::= static? entity-kind context entity-name
   if (decl->isStatic())
     Buffer << 'Z';
@@ -1603,7 +1603,12 @@ void Mangler::mangleEntity(const ValueDecl *decl,
       return mangleAccessorEntity(accessorKind, func->getAddressorKind(),
                                   func->getAccessorStorageDecl());
   }
-  
+
+  // Avoid mangling nameless entity. This may happen in erroneous code as code
+  // completion.
+  if (!decl->hasName())
+    return;
+
   if (isa<VarDecl>(decl)) {
     Buffer << 'v';
   } else if (isa<SubscriptDecl>(decl)) {
diff --git a/validation-test/IDE/crashers/016-swift-mangle-mangler-mangleidentifier.swift b/validation-test/IDE/crashers/016-swift-mangle-mangler-mangleidentifier.swift
deleted file mode 100644
index 207dc5daa3507..0000000000000
--- a/validation-test/IDE/crashers/016-swift-mangle-mangler-mangleidentifier.swift
+++ /dev/null
@@ -1,3 +0,0 @@
-// RUN: not --crash %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
-// REQUIRES: asserts
-var d{let:{func a#^A^#
diff --git a/validation-test/IDE/crashers/100-swift-mangle-mangler-mangledeclname.swift b/validation-test/IDE/crashers/100-swift-mangle-mangler-mangledeclname.swift
deleted file mode 100644
index 16c6814c63438..0000000000000
--- a/validation-test/IDE/crashers/100-swift-mangle-mangler-mangledeclname.swift
+++ /dev/null
@@ -1,3 +0,0 @@
-// RUN: not --crash %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
-// REQUIRES: asserts
-{let:{class S(}#^A^#
\ No newline at end of file
diff --git a/validation-test/IDE/crashers_fixed/016-swift-mangle-mangler-mangleidentifier.swift b/validation-test/IDE/crashers_fixed/016-swift-mangle-mangler-mangleidentifier.swift
new file mode 100644
index 0000000000000..10652d26ef427
--- /dev/null
+++ b/validation-test/IDE/crashers_fixed/016-swift-mangle-mangler-mangleidentifier.swift
@@ -0,0 +1,3 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+// REQUIRES: asserts
+var d{let:{func a#^A^#
diff --git a/validation-test/IDE/crashers_fixed/100-swift-mangle-mangler-mangledeclname.swift b/validation-test/IDE/crashers_fixed/100-swift-mangle-mangler-mangledeclname.swift
new file mode 100644
index 0000000000000..75cc436ba073c
--- /dev/null
+++ b/validation-test/IDE/crashers_fixed/100-swift-mangle-mangler-mangledeclname.swift
@@ -0,0 +1,2 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+{let:{class S(}#^A^#