diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index a95d082..0535923 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -853,12 +853,18 @@
     if (Diags.getDiagnosticLevel(diag::warn_unused_parameter) == 
           Diagnostic::Ignored)
       return;
+
+    // Don't diagnose unused-parameter errors in template instantiations; we
+    // will already have done so in the template itself.
+    if (!ActiveTemplateInstantiations.empty())
+      return;
     
     for (; Param != ParamEnd; ++Param) {
       if (!(*Param)->isUsed() && (*Param)->getDeclName() &&
-          !(*Param)->template hasAttr<UnusedAttr>())
+          !(*Param)->template hasAttr<UnusedAttr>()) {
         Diag((*Param)->getLocation(), diag::warn_unused_parameter)
           << (*Param)->getDeclName();
+      }
     }
   }