diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -1495,6 +1495,13 @@
   // initializers throws an exception.
   SmallVector<EHScopeStack::stable_iterator, 16> cleanups;
   llvm::Instruction *cleanupDominator = nullptr;
+  auto addCleanup = [&](const EHScopeStack::stable_iterator &cleanup) {
+    cleanups.push_back(cleanup);
+    if (!cleanupDominator) // create placeholder once needed
+      cleanupDominator = CGF.Builder.CreateAlignedLoad(
+          CGF.Int8Ty, llvm::Constant::getNullValue(CGF.Int8PtrTy),
+          CharUnits::One());
+  };
 
   unsigned curInitIndex = 0;
 
@@ -1519,7 +1526,7 @@
       if (QualType::DestructionKind dtorKind =
               Base.getType().isDestructedType()) {
         CGF.pushDestroy(dtorKind, V, Base.getType());
-        cleanups.push_back(CGF.EHStack.stable_begin());
+        addCleanup(CGF.EHStack.stable_begin());
       }
     }
   }
@@ -1596,15 +1603,9 @@
           = field->getType().isDestructedType()) {
       assert(LV.isSimple());
       if (CGF.needsEHCleanup(dtorKind)) {
-        if (!cleanupDominator)
-          cleanupDominator = CGF.Builder.CreateAlignedLoad(
-              CGF.Int8Ty,
-              llvm::Constant::getNullValue(CGF.Int8PtrTy),
-              CharUnits::One()); // placeholder
-
         CGF.pushDestroy(EHCleanup, LV.getAddress(), field->getType(),
                         CGF.getDestroyer(dtorKind), false);
-        cleanups.push_back(CGF.EHStack.stable_begin());
+        addCleanup(CGF.EHStack.stable_begin());
         pushedCleanup = true;
       }
     }
@@ -1620,6 +1621,8 @@
 
   // Deactivate all the partial cleanups in reverse order, which
   // generally means popping them.
+  assert((cleanupDominator || cleanups.empty()) &&
+         "Missing cleanupDominator before deactivating cleanup blocks");
   for (unsigned i = cleanups.size(); i != 0; --i)
     CGF.DeactivateCleanupBlock(cleanups[i-1], cleanupDominator);
 
diff --git a/clang/test/CodeGenCXX/pr40771-ctad-with-lambda-copy-capture.cpp b/clang/test/CodeGenCXX/pr40771-ctad-with-lambda-copy-capture.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenCXX/pr40771-ctad-with-lambda-copy-capture.cpp
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -emit-obj --std=c++17 -fcxx-exceptions -fexceptions %s
+// PR40771: check that this input does not crash or assert
+
+struct Q { Q(); };
+struct R { R(Q); ~R(); };
+struct S { S(Q); ~S(); };
+struct T : R, S {};
+
+Q q;
+T t { R{q}, S{q} };