diff --git a/mlir/test/mlir-tblgen/op-format-spec.td b/mlir/test/mlir-tblgen/op-format-spec.td
--- a/mlir/test/mlir-tblgen/op-format-spec.td
+++ b/mlir/test/mlir-tblgen/op-format-spec.td
@@ -280,26 +280,32 @@
 // Coverage Checks
 //===----------------------------------------------------------------------===//
 
-// CHECK: error: format missing instance of result #0('result') type
+// CHECK: error: Type of result #0, named 'result', is not buildable and a buildable type cannot be inferred from other types.  Suggest adding a type constraint to the operation or adding a 'type($result)' directive to the custom assembly format.
 def ZCoverageInvalidA : TestFormat_Op<"variable_invalid_a", [{
   attr-dict
 }]>, Arguments<(ins AnyMemRef:$operand)>, Results<(outs AnyMemRef:$result)>;
-// CHECK: error: format missing instance of operand #0('operand')
+// CHECK: error: Operand #0, named 'operand', not found. Suggest adding a '$operand' directive to the custom assembly format.
 def ZCoverageInvalidB : TestFormat_Op<"variable_invalid_b", [{
   type($result) attr-dict
 }]>, Arguments<(ins AnyMemRef:$operand)>, Results<(outs AnyMemRef:$result)>;
-// CHECK: error: format missing instance of operand #0('operand') type
+// CHECK: error: Type of operand #0, named 'operand', is not buildable and a buildable type cannot be inferred from other types.  Suggest adding a type constraint to the operation or adding a 'type($operand)' directive to the custom assembly format.
 def ZCoverageInvalidC : TestFormat_Op<"variable_invalid_c", [{
   $operand type($result) attr-dict
 }]>, Arguments<(ins AnyMemRef:$operand)>, Results<(outs AnyMemRef:$result)>;
-// CHECK: error: format missing instance of operand #0('operand') type
+// CHECK: error: Type of operand #0, named 'operand', is not buildable and a buildable type cannot be inferred from other types.  Suggest adding a type constraint to the operation or adding a 'type($operand)' directive to the custom assembly format.
 def ZCoverageInvalidD : TestFormat_Op<"variable_invalid_d", [{
   operands attr-dict
 }]>, Arguments<(ins Variadic<I64>:$operand)>;
-// CHECK: error: format missing instance of result #0('result') type
+// CHECK: error: Type of result #0, named 'result', is not buildable and a buildable type cannot be inferred from other types.  Suggest adding a type constraint to the operation or adding a 'type($result)' directive to the custom assembly format.
 def ZCoverageInvalidE : TestFormat_Op<"variable_invalid_e", [{
   attr-dict
 }]>, Results<(outs Variadic<I64>:$result)>;
+// CHECK: error: Successor #0, named 'successor', not found. Suggest adding a '$successor' directive to the custom assembly format.
+def ZCoverageInvalidF : TestFormat_Op<"variable_invalid_f", [{
+	 attr-dict
+}]> {
+  let successors = (successor AnySuccessor:$successor);
+}
 // CHECK-NOT: error
 def ZCoverageValidA : TestFormat_Op<"variable_valid_a", [{
   $operand type($operand) type($result) attr-dict
diff --git a/mlir/tools/mlir-tblgen/OpFormatGen.cpp b/mlir/tools/mlir-tblgen/OpFormatGen.cpp
--- a/mlir/tools/mlir-tblgen/OpFormatGen.cpp
+++ b/mlir/tools/mlir-tblgen/OpFormatGen.cpp
@@ -1337,7 +1337,7 @@
 
   // Check that the attribute dictionary is in the format.
   if (!hasAttrDict)
-    return emitError(loc, "format missing 'attr-dict' directive");
+    return emitError(loc, "format missing 'attr-dict' directive.");
 
   // Check for any type traits that we can use for inferring types.
   llvm::StringMap<TypeResolutionInstance> variableTyResolver;
@@ -1377,8 +1377,13 @@
       NamedTypeConstraint &result = op.getResult(i);
       Optional<StringRef> builder = result.constraint.getBuilderCall();
       if (!builder || result.constraint.isVariadic()) {
-        return emitError(loc, "format missing instance of result #" + Twine(i) +
-                                  "('" + result.name + "') type");
+        return emitError(loc, "Type of result #" + Twine(i) +
+                       ", named '" + result.name +
+                       "', is not buildable and a buildable type cannot " +
+                       "be inferred from other types.  Suggest adding a " +
+                       "type constraint to the operation or adding a " +
+                       "'type($" + result.name + ")' directive to the " +
+                       "custom assembly format.");
       }
       // Note in the format that this result uses the custom builder.
       auto it = buildableTypes.insert({*builder, buildableTypes.size()});
@@ -1393,8 +1398,10 @@
 
     // Check that the operand itself is in the format.
     if (!hasAllOperands && !seenOperands.count(&operand)) {
-      return emitError(loc, "format missing instance of operand #" + Twine(i) +
-                                "('" + operand.name + "')");
+      return emitError(loc, "Operand #" + Twine(i) +
+                       ", named '" + operand.name + "', not found." +
+                       " Suggest adding a '$" + operand.name +
+                       "' directive to the custom assembly format.");
     }
 
     // Check that the operand type is in the format, or that it can be inferred.
@@ -1413,8 +1420,13 @@
     // we aren't using the 'operands' directive.
     Optional<StringRef> builder = operand.constraint.getBuilderCall();
     if (!builder || (hasAllOperands && operand.isVariadic())) {
-      return emitError(loc, "format missing instance of operand #" + Twine(i) +
-                                "('" + operand.name + "') type");
+      return emitError(loc, "Type of operand #" + Twine(i) +
+                       ", named '" + operand.name +
+                       "', is not buildable and a buildable type cannot " +
+                       "be inferred from other types.  Suggest adding a " +
+                       "type constraint to the operation or adding a " +
+                       "'type($" + operand.name + ")' directive to the " +
+                       "custom assembly format.");
     }
     auto it = buildableTypes.insert({*builder, buildableTypes.size()});
     fmt.operandTypes[i].setBuilderIdx(it.first->second);
@@ -1425,8 +1437,10 @@
     for (unsigned i = 0, e = op.getNumSuccessors(); i != e; ++i) {
       const NamedSuccessor &successor = op.getSuccessor(i);
       if (!seenSuccessors.count(&successor)) {
-        return emitError(loc, "format missing instance of successor #" +
-                                  Twine(i) + "('" + successor.name + "')");
+        return emitError(loc, "Successor #" + Twine(i) +
+                         ", named '" + successor.name + "', not found." +
+                         " Suggest adding a '$" + successor.name +
+                         "' directive to the custom assembly format.");
       }
     }
   }