Index: llvm/lib/AsmParser/LLParser.cpp
===================================================================
--- llvm/lib/AsmParser/LLParser.cpp
+++ llvm/lib/AsmParser/LLParser.cpp
@@ -3439,9 +3439,24 @@
   // Set the name on the instruction.
   Inst->setName(NameStr);
 
-  if (Inst->getName() != NameStr)
+  if (Inst->getName() != NameStr) {
+
+    size_t InstNameSize = Inst->getName().size();
+    size_t NameStrSize = NameStr.size();
+
+    if (InstNameSize != NameStrSize + 1) {
+      // The name is too long and was trimmed when stored in SmallString with
+      // NonGlobalValueMaxNameSize
+      return P.error(NameLoc,
+                     "name is too long and exceeds non global max name size, "
+                     "consider making the name shorter or "
+                     "increasing -non-global-value-max-name-size: '" +
+                         NameStr + "'");
+    }
+
     return P.error(NameLoc, "multiple definition of local value named '" +
                                 NameStr + "'");
+  }
   return false;
 }
 
Index: llvm/test/Assembler/non-global-value-max-name-size-2.ll
===================================================================
--- /dev/null
+++ llvm/test/Assembler/non-global-value-max-name-size-2.ll
@@ -0,0 +1,16 @@
+; RUN: llvm-as %s -non-global-value-max-name-size=18
+; RUN: not llvm-as %s -non-global-value-max-name-size=5 2>&1 | FileCheck %s
+
+; CHECK: error: name is too long and exceeds non global max name size
+; CHECK: 'varname.too.long.1'
+
+
+define void @f() {
+entry:
+  %var.1 = alloca i32, align 4
+  br label %bb.rt
+
+bb.rt:
+  %varname.too.long.1 = add i32 0, 5
+  ret void
+}