Move diagnostic from parser to later phase.

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

@@ -2920,17 +2920,6 @@ private bool IsEndOfNameInExplicitInterface()
                     // our context again (perhaps an open brace).
                 }
 
-                // When a generic method overrides a generic method declared in a base
-                // class, or is an explicit interface member implementation of a method in
-                // a base interface, the method shall not specify any type-parameter-
-                // constraints-clauses. In these cases, the type parameters of the method
-                // inherit constraints from the method being overridden or implemented
-                if (!constraints.IsNull && constraints.Count > 0 &&
-                    ((explicitInterfaceOpt != null) || (modifiers != null && modifiers.Any((int)SyntaxKind.OverrideKeyword))))
-                {
-                    constraints[0] = this.AddErrorToFirstToken(constraints[0], ErrorCode.ERR_OverrideWithConstraints);
-                }
-
                 _termState = saveTerm;
 
                 BlockSyntax blockBody;

src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberMethodSymbol.cs

@@ -113,6 +113,22 @@ internal sealed class SourceMemberMethodSymbol : SourceMethodSymbol
             {
                 diagnostics.Add(info, location);
             }
+
+            // When a generic method overrides a generic method declared in a base class, or is an 
+            // explicit interface member implementation of a method in a base interface, the method
+            // shall not specify any type-parameter-constraints-clauses. In these cases, the type 
+            // parameters of the method inherit constraints from the method being overridden or 
+            // implemented
+            if (syntax.ConstraintClauses.Count > 0)
+            {
+                if (syntax.ExplicitInterfaceSpecifier != null ||
+                    syntax.Modifiers.Any(SyntaxKind.OverrideKeyword))
+                {
+                    diagnostics.Add(
+                        ErrorCode.ERR_OverrideWithConstraints, 
+                        syntax.ConstraintClauses[0].WhereKeyword.GetLocation());
+                }
+            }
         }
 
         public override bool ReturnsVoid