Index: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7821,6 +7821,8 @@
   "sampler_t variable required - got %0">;
 def err_wrong_sampler_addressspace: Error<
   "sampler type cannot be used with the __local and __global address space qualifiers">;
+def error_opencl_cast_non_zero_to_event_t : Error<
+  "cannot cast non-zero value '%0' to 'event_t'">;
 def err_opencl_global_invalid_addr_space : Error<
   "%select{program scope|static local|extern}0 variable must reside in %1 address space">;
 def err_missing_actual_pipe_type : Error<
Index: cfe/trunk/lib/Sema/SemaCast.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaCast.cpp
+++ cfe/trunk/lib/Sema/SemaCast.cpp
@@ -2441,6 +2441,22 @@
       return;
     }
 
+    // OpenCL v2.0 s6.13.10 - Allow casts from '0' to event_t type.
+    if (Self.getLangOpts().OpenCL && DestType->isEventT()) {
+      llvm::APSInt CastInt;
+      if (SrcExpr.get()->EvaluateAsInt(CastInt, Self.Context)) {
+        if (0 == CastInt) {
+          Kind = CK_ZeroToOCLEvent;
+          return;
+        }
+        Self.Diag(OpRange.getBegin(),
+                  diag::error_opencl_cast_non_zero_to_event_t)
+                  << CastInt.toString(10) << SrcExpr.get()->getSourceRange();
+        SrcExpr = ExprError();
+        return;
+      }
+    }
+
     // Reject any other conversions to non-scalar types.
     Self.Diag(OpRange.getBegin(), diag::err_typecheck_cond_expect_scalar)
       << DestType << SrcExpr.get()->getSourceRange();
Index: cfe/trunk/test/CodeGenOpenCL/event_t.cl
===================================================================
--- cfe/trunk/test/CodeGenOpenCL/event_t.cl
+++ cfe/trunk/test/CodeGenOpenCL/event_t.cl
@@ -9,4 +9,6 @@
 // CHECK: call {{.*}}void @foo(%opencl.event_t* %
   foo(0);
 // CHECK: call {{.*}}void @foo(%opencl.event_t* null)
+  foo((event_t)0);
+// CHECK: call {{.*}}void @foo(%opencl.event_t* null)
 }
Index: cfe/trunk/test/SemaOpenCL/event_t.cl
===================================================================
--- cfe/trunk/test/SemaOpenCL/event_t.cl
+++ cfe/trunk/test/SemaOpenCL/event_t.cl
@@ -14,5 +14,6 @@
   foo(e);
   foo(0);
   foo(5); // expected-error {{passing 'int' to parameter of incompatible type 'event_t'}}
+  foo((event_t)1); // expected-error {{cannot cast non-zero value '1' to 'event_t'}}
 }