diff --git a/mlir/lib/Parser/Parser.cpp b/mlir/lib/Parser/Parser.cpp
index 3a817e9231a3..b9b903cd2b5e 100644
--- a/mlir/lib/Parser/Parser.cpp
+++ b/mlir/lib/Parser/Parser.cpp
@@ -1785,7 +1785,20 @@ public:
     // Handle delimiters.
     switch (delimiter) {
     case Delimiter::None:
-      break;
+      // Don't check for the absence of a delimiter if the number of operands
+      // is unknown (and hence the operand list could be empty).
+      if (requiredOperandCount == -1)
+        break;
+      // Token already matches an identifier and so can't be a delimiter.
+      if (parser.getToken().is(Token::percent_identifier))
+        break;
+      // Test against known delimiters.
+      if (parser.getToken().is(Token::l_paren) ||
+          parser.getToken().is(Token::l_square))
+        return emitError(startLoc, "unexpected delimiter");
+      return emitError(startLoc, "unable to parse '" +
+                                     parser.getTokenSpelling() +
+                                     "' as operand");
     case Delimiter::OptionalParen:
       if (parser.getToken().isNot(Token::l_paren))
         return false;
diff --git a/mlir/test/IR/invalid-ops.mlir b/mlir/test/IR/invalid-ops.mlir
index 62944e4ac6f6..1e4e6965c439 100644
--- a/mlir/test/IR/invalid-ops.mlir
+++ b/mlir/test/IR/invalid-ops.mlir
@@ -126,5 +126,20 @@ mlfunc @calls(%arg0 : i32) {
 
 cfgfunc @cfgfunc_with_ops(f32) {
 bb0(%a : f32):
-  %sf = addf(%a, %a) : f32  // expected-error {{custom op 'addf' expected 2 operands}}
+  %sf = addf %a, %a, %a : f32  // expected-error {{custom op 'addf' expected 2 operands}}
 }
+
+// -----
+
+cfgfunc @cfgfunc_with_ops(f32) {
+bb0(%a : f32):
+  %sf = addf(%a, %a) : f32  // expected-error {{unexpected delimiter}}
+}
+
+// -----
+
+cfgfunc @cfgfunc_with_ops(f32) {
+bb0(%a : f32):
+  %sf = addf{%a, %a} : f32  // expected-error {{unable to parse '{' as operand}}
+}
+