diff --git a/llvm/include/llvm/IR/Metadata.h b/llvm/include/llvm/IR/Metadata.h
--- a/llvm/include/llvm/IR/Metadata.h
+++ b/llvm/include/llvm/IR/Metadata.h
@@ -897,6 +897,7 @@
 class MDNode : public Metadata {
   friend class ReplaceableMetadataImpl;
   friend class LLVMContextImpl;
+  friend class DIArgList;
 
   unsigned NumOperands;
   unsigned NumUnresolved;
diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -1642,6 +1642,11 @@
   assert((!New || isa<ValueAsMetadata>(New)) &&
          "DIArgList must be passed a ValueAsMetadata");
   untrack();
+  bool Uniq = isUniqued();
+  if (Uniq)
+    // We need to update the uniqueness once the Args are updated since they
+    // form the key to the DIArgLists store.
+    eraseFromStore();
   ValueAsMetadata *NewVM = cast_or_null<ValueAsMetadata>(New);
   for (ValueAsMetadata *&VM : Args) {
     if (&VM == OldVMPtr) {
@@ -1651,6 +1656,11 @@
         VM = ValueAsMetadata::get(UndefValue::get(VM->getValue()->getType()));
     }
   }
+  if (Uniq) {
+    auto *Uniqued = uniquify();
+    if (Uniqued != this)
+      storeDistinctInContext();
+  }
   track();
 }
 void DIArgList::track() {
diff --git a/llvm/lib/IR/LLVMContextImpl.cpp b/llvm/lib/IR/LLVMContextImpl.cpp
--- a/llvm/lib/IR/LLVMContextImpl.cpp
+++ b/llvm/lib/IR/LLVMContextImpl.cpp
@@ -55,8 +55,15 @@
 
   // Drop references for MDNodes.  Do this before Values get deleted to avoid
   // unnecessary RAUW when nodes are still unresolved.
-  for (auto *I : DistinctMDNodes)
+  for (auto *I : DistinctMDNodes) {
+    // We may have DIArgList that were uniqued, and as it has a custom
+    // implementation of dropAllReferences, it needs to be explicitly invoked.
+    if (auto *AL = dyn_cast<DIArgList>(I)) {
+      AL->dropAllReferences();
+      continue;
+    }
     I->dropAllReferences();
+  }
 #define HANDLE_MDNODE_LEAF_UNIQUABLE(CLASS)                                    \
   for (auto *I : CLASS##s)                                                     \
     I->dropAllReferences();