diff --git a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
--- a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -843,18 +843,13 @@
     std::vector<ValueInfo> &TargetsForSlot, const TypeIdCompatibleVtableInfo TIdInfo,
     uint64_t ByteOffset) {
   for (const TypeIdOffsetVtableInfo &P : TIdInfo) {
-    // Ensure that we have at most one external linkage vtable initializer.
-    assert(P.VTableVI.getSummaryList().size() == 1 ||
-           llvm::count_if(
-               P.VTableVI.getSummaryList(),
-               [&](const std::unique_ptr<GlobalValueSummary> &Summary) {
-                 return GlobalValue::isExternalLinkage(Summary->linkage());
-               }) <= 1);
     // Find the first non-available_externally linkage vtable initializer.
     // We can have multiple available_externally, linkonce_odr and weak_odr
     // vtable initializers, however we want to skip available_externally as they
     // do not have type metadata attached, and therefore the summary will not
-    // contain any vtable functions.
+    // contain any vtable functions. We can also have multiple external
+    // vtable initializers in the case of comdats, which we cannot check here.
+    // The linker should give an error in this case.
     //
     // Also, handle the case of same-named local Vtables with the same path
     // and therefore the same GUID. This can happen if there isn't enough
diff --git a/llvm/test/ThinLTO/X86/Inputs/devirt_external_comdat_same_guid.ll b/llvm/test/ThinLTO/X86/Inputs/devirt_external_comdat_same_guid.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/Inputs/devirt_external_comdat_same_guid.ll
@@ -0,0 +1,43 @@
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+source_filename = "-"
+
+%struct.A = type { i32 (...)** }
+%struct.B = type { %struct.A }
+
+$_ZTV1B = comdat any
+
+@_ZTV1B = constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.B*, i32)* @_ZN1B1fEi to i8*), i8* bitcast (i32 (%struct.A*, i32)* @_ZN1A1nEi to i8*)] }, comdat, !type !0, !type !1
+
+define i32 @_ZN1B1fEi(%struct.B* %this, i32 %a) #0 comdat($_ZTV1B) {
+   ret i32 0;
+}
+
+define i32 @_ZN1A1nEi(%struct.A* %this, i32 %a) #0 comdat($_ZTV1B) {
+   ret i32 0;
+}
+
+define i32 @test2(%struct.B* %obj, i32 %a) {
+entry:
+  %0 = bitcast %struct.B* %obj to i8***
+  %vtable2 = load i8**, i8*** %0
+  %1 = bitcast i8** %vtable2 to i8*
+  %p2 = call i1 @llvm.type.test(i8* %1, metadata !"_ZTS1B")
+  call void @llvm.assume(i1 %p2)
+
+  %fptrptr = getelementptr i8*, i8** %vtable2, i32 1
+  %2 = bitcast i8** %fptrptr to i32 (%struct.B*, i32)**
+  %fptr33 = load i32 (%struct.B*, i32)*, i32 (%struct.B*, i32)** %2, align 8
+
+  %call4 = tail call i32 %fptr33(%struct.B* nonnull %obj, i32 %a)
+  ret i32 %call4
+}
+
+attributes #0 = { noinline optnone }
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1)
+
+!0 = !{i64 16, !"_ZTS1A"}
+!1 = !{i64 16, !"_ZTS1B"}
diff --git a/llvm/test/ThinLTO/X86/devirt_external_comdat_same_guid.ll b/llvm/test/ThinLTO/X86/devirt_external_comdat_same_guid.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/devirt_external_comdat_same_guid.ll
@@ -0,0 +1,87 @@
+; REQUIRES: x86-registered-target
+
+; Test that index-based devirtualization in the presence of external
+; vtables with the same name (with comdat) succeeds.
+
+; Generate unsplit module with summary for ThinLTO index-based WPD.
+; RUN: opt -thinlto-bc -o %t3.o %s
+; RUN: opt -thinlto-bc -o %t4.o %p/Inputs/devirt_external_comdat_same_guid.ll
+
+; RUN: llvm-lto2 run %t3.o %t4.o -save-temps -use-new-pm -pass-remarks=. \
+; RUN:   -wholeprogramdevirt-print-index-based \
+; RUN:   -o %t5 \
+; RUN:   -r=%t3.o,use_B,px \
+; RUN:   -r=%t3.o,test,px \
+; RUN:   -r=%t3.o,_ZTV1B,px \
+; RUN:   -r=%t3.o,_ZN1B1fEi,px \
+; RUN:   -r=%t3.o,_ZN1B1nEi,px \
+; RUN:   -r=%t4.o,_ZTV1B,x \
+; RUN:   -r=%t4.o,_ZN1B1fEi,x \
+; RUN:   -r=%t4.o,_ZN1A1nEi,x \
+; RUN:   -r=%t4.o,test2,px \
+; RUN:   2>&1 | FileCheck %s --check-prefix=REMARK --check-prefix=PRINT
+; RUN: llvm-dis %t5.1.4.opt.bc -o - | FileCheck %s --check-prefix=CHECK-IR1
+; RUN: llvm-dis %t5.2.4.opt.bc -o - | FileCheck %s --check-prefix=CHECK-IR2
+
+; PRINT-DAG: Devirtualized call to {{.*}} (_ZN1A1nEi)
+
+; REMARK-DAG: single-impl: devirtualized a call to _ZN1A1nEi
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+source_filename = "-"
+
+%struct.A = type { i32 (...)** }
+%struct.B = type { %struct.A }
+
+$_ZTV1B = comdat any
+
+@_ZTV1B = constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.B*, i32)* @_ZN1B1fEi to i8*), i8* bitcast (i32 (%struct.B*, i32)* @_ZN1B1nEi to i8*)] }, comdat, !type !0, !type !1
+
+define i32 @_ZN1B1fEi(%struct.B* %this, i32 %a) #0 comdat($_ZTV1B) {
+   ret i32 0;
+}
+
+define i32 @_ZN1B1nEi(%struct.B* %this, i32 %a) #0 comdat($_ZTV1B) {
+   ret i32 0;
+}
+
+; Ensures that vtable of B is live so that we will attempt devirt.
+define dso_local i32 @use_B(%struct.B* %a) {
+entry:
+  %0 = bitcast %struct.B* %a to i32 (...)***
+  store i32 (...)** bitcast (i8** getelementptr inbounds ({ [4 x i8*] }, { [4 x i8*] }* @_ZTV1B, i64 0, inrange i32 0, i64 2) to i32 (...)**), i32 (...)*** %0, align 8
+  ret i32 0
+}
+
+; CHECK-IR1: define i32 @test(
+define i32 @test(%struct.A* %obj, i32 %a) {
+entry:
+  %0 = bitcast %struct.A* %obj to i8***
+  %vtable = load i8**, i8*** %0
+  %1 = bitcast i8** %vtable to i8*
+  %p = call i1 @llvm.type.test(i8* %1, metadata !"_ZTS1A")
+  call void @llvm.assume(i1 %p)
+  %fptrptr = getelementptr i8*, i8** %vtable, i32 1
+  %2 = bitcast i8** %fptrptr to i32 (%struct.A*, i32)**
+  %fptr1 = load i32 (%struct.A*, i32)*, i32 (%struct.A*, i32)** %2, align 8
+
+  ; Check that the call was devirtualized.
+  ; CHECK-IR1: tail call i32 {{.*}}@_ZN1A1nEi
+  %call = tail call i32 %fptr1(%struct.A* nonnull %obj, i32 %a)
+
+  ret i32 %call
+}
+
+; CHECK-IR2: define i32 @test2
+; Check that the call was devirtualized.
+; CHECK-IR2:   tail call i32 @_ZN1A1nEi
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1)
+
+attributes #0 = { noinline optnone }
+
+!0 = !{i64 16, !"_ZTS1A"}
+!1 = !{i64 16, !"_ZTS1B"}