diff --git a/llvm/lib/MC/MCParser/MasmParser.cpp b/llvm/lib/MC/MCParser/MasmParser.cpp
--- a/llvm/lib/MC/MCParser/MasmParser.cpp
+++ b/llvm/lib/MC/MCParser/MasmParser.cpp
@@ -1122,8 +1122,22 @@
   }
 
   const AsmToken *tok = &Lexer.Lex();
+  bool StartOfStatement = Lexer.isAtStartOfStatement();
 
   while (tok->is(AsmToken::Identifier)) {
+    if (StartOfStatement) {
+      AsmToken NextTok;
+
+      MutableArrayRef<AsmToken> Buf(NextTok);
+      size_t ReadCount = Lexer.peekTokens(Buf);
+      if (ReadCount && NextTok.is(AsmToken::Identifier) &&
+          (NextTok.getString().equals_lower("equ") ||
+           NextTok.getString().equals_lower("textequ"))) {
+        // This looks like an EQU or TEXTEQU directive; don't expand the
+        // identifier, allowing for redefinitions.
+        break;
+      }
+    }
     auto it = Variables.find(tok->getIdentifier().lower());
     const llvm::MCAsmMacro *M =
         getContext().lookupMacro(tok->getIdentifier().lower());
@@ -3327,35 +3341,38 @@
 ///  ::= name "=" expression
 ///    | name "equ" expression    (not redefinable)
 ///    | name "equ" text-list
-///    | name "textequ" text-list
+///    | name "textequ" text-list (redefinability unspecified)
 bool MasmParser::parseDirectiveEquate(StringRef IDVal, StringRef Name,
                                       DirectiveKind DirKind) {
   Variable &Var = Variables[Name.lower()];
   if (Var.Name.empty()) {
     Var.Name = Name;
-  } else if (!Var.Redefinable) {
-    return TokError("invalid variable redefinition");
   }
-  Var.Redefinable = (DirKind != DK_EQU);
 
   SMLoc StartLoc = Lexer.getLoc();
   if (DirKind == DK_EQU || DirKind == DK_TEXTEQU) {
     // "equ" and "textequ" both allow text expressions.
     std::string Value;
-    if (!parseTextItem(Value)) {
-      Var.IsText = true;
-      Var.TextValue = Value;
+    std::string TextItem;
+    if (!parseTextItem(TextItem)) {
+      Value += TextItem;
 
       // Accept a text-list, not just one text-item.
       auto parseItem = [&]() -> bool {
-        if (parseTextItem(Value))
+        if (parseTextItem(TextItem))
           return TokError("expected text item");
-        Var.TextValue += Value;
+        Value += TextItem;
         return false;
       };
       if (parseOptionalToken(AsmToken::Comma) && parseMany(parseItem))
         return addErrorSuffix(" in '" + Twine(IDVal) + "' directive");
 
+      if (!Var.Redefinable && (!Var.IsText || Var.TextValue != Value))
+        return Error(getTok().getLoc(), "invalid variable redefinition");
+      Var.IsText = true;
+      Var.TextValue = Value;
+      Var.Redefinable = true;
+
       return false;
     }
   }
@@ -3367,19 +3384,28 @@
   SMLoc EndLoc;
   if (parseExpression(Expr, EndLoc))
     return addErrorSuffix(" in '" + Twine(IDVal) + "' directive");
+
+  int64_t Value;
+  if (!Expr->evaluateAsAbsolute(Value, getStreamer().getAssemblerPtr())) {
+    // Not an absolute expression; define as a text replacement.
+    StringRef ExprAsString = StringRef(
+        StartLoc.getPointer(), EndLoc.getPointer() - StartLoc.getPointer());
+    if (!Var.Redefinable && (!Var.IsText && Var.TextValue != ExprAsString))
+      return Error(getTok().getLoc(), "invalid variable redefinition");
+    Var.IsText = true;
+    Var.TextValue = ExprAsString.str();
+  } else {
+    if (!Var.Redefinable && (Var.IsText || Var.NumericValue != Value))
+      return Error(getTok().getLoc(), "invalid variable redefinition");
+    Var.NumericValue = Value;
+  }
+  Var.Redefinable = (DirKind == DK_ASSIGN);
+
   MCSymbol *Sym = getContext().getOrCreateSymbol(Var.Name);
   Sym->setRedefinable(Var.Redefinable);
   Sym->setVariableValue(Expr);
   Sym->setExternal(false);
 
-  if (Expr->evaluateAsAbsolute(Var.NumericValue,
-                               getStreamer().getAssemblerPtr()))
-    return false;
-
-  // Not an absolute expression; define as a text replacement.
-  Var.IsText = true;
-  Var.TextValue = StringRef(StartLoc.getPointer(),
-                            EndLoc.getPointer() - StartLoc.getPointer()).str();
   return false;
 }
 
diff --git a/llvm/test/tools/llvm-ml/variable_redef.asm b/llvm/test/tools/llvm-ml/variable_redef.asm
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-ml/variable_redef.asm
@@ -0,0 +1,76 @@
+; RUN: llvm-ml -filetype=s %s /Fo - | FileCheck %s
+
+.data
+
+; <var> = <expression> can be redefined at any time.
+assigned_number = 1
+t1_original BYTE assigned_number
+assigned_number = 1
+t1_reset BYTE assigned_number
+assigned_number = 2
+t1_changed BYTE assigned_number
+
+; CHECK-LABEL: t1_original:
+; CHECK-NEXT: .byte 1
+
+; CHECK-LABEL: t1_reset:
+; CHECK-NEXT: .byte 1
+
+; CHECK-LABEL: t1_changed:
+; CHECK-NEXT: .byte 2
+
+; <var> EQU <expression> can be redundantly set, but can't be changed.
+equated_number equ 3
+t2_original BYTE equated_number
+equated_number equ 3
+t2_reset BYTE equated_number
+
+; CHECK-LABEL: t2_original:
+; CHECK-NEXT: .byte 3
+
+; CHECK-LABEL: t2_reset:
+; CHECK-NEXT: .byte 3
+
+; <var> EQU <text> can be redefined at any time.
+equated_text equ <4, 5>
+t3_original BYTE equated_text
+equated_text equ <4, 5>
+t3_reset BYTE equated_text
+equated_text equ <5, 6>
+t3_changed BYTE equated_text
+
+; CHECK-LABEL: t3_original:
+; CHECK-NEXT: .byte 4
+; CHECK-NEXT: .byte 5
+
+; CHECK-LABEL: t3_reset:
+; CHECK-NEXT: .byte 4
+; CHECK-NEXT: .byte 5
+
+; CHECK-LABEL: t3_changed:
+; CHECK-NEXT: .byte 5
+; CHECK-NEXT: .byte 6
+
+; <var> TEXTEQU <text> can be redefined at any time.
+textequated_text textequ <7, 8>
+t4_original BYTE textequated_text
+textequated_text textequ <7, 8>
+t4_reset BYTE textequated_text
+textequated_text textequ <9, 10>
+t4_changed BYTE textequated_text
+
+; CHECK-LABEL: t4_original:
+; CHECK-NEXT: .byte 7
+; CHECK-NEXT: .byte 8
+
+; CHECK-LABEL: t4_reset:
+; CHECK-NEXT: .byte 7
+; CHECK-NEXT: .byte 8
+
+; CHECK-LABEL: t4_changed:
+; CHECK-NEXT: .byte 9
+; CHECK-NEXT: .byte 10
+
+.code
+
+end
diff --git a/llvm/test/tools/llvm-ml/variable_redef_errors.asm b/llvm/test/tools/llvm-ml/variable_redef_errors.asm
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-ml/variable_redef_errors.asm
@@ -0,0 +1,12 @@
+; RUN: not llvm-ml -filetype=s %s /Fo - 2>&1 | FileCheck %s --implicit-check-not=error:
+
+.data
+
+; <var> EQU <expression> can't be redefined to a new value
+equated_number equ 3
+; CHECK: :[[# @LINE + 1]]:21: error: invalid variable redefinition
+equated_number equ 4
+
+.code
+
+end