diff --git a/test/behavior.zig b/test/behavior.zig
index 81f2c5dd00..b9cfeb8e0b 100644
--- a/test/behavior.zig
+++ b/test/behavior.zig
@@ -1,3 +1,5 @@
+const builtin = @import("builtin");
+
 comptime {
     _ = @import("cases/align.zig");
     _ = @import("cases/alignof.zig");
@@ -11,7 +13,6 @@ comptime {
     _ = @import("cases/bugs/656.zig");
     _ = @import("cases/cast.zig");
     _ = @import("cases/const_slice_child.zig");
-    _ = @import("cases/coroutines.zig");
     _ = @import("cases/defer.zig");
     _ = @import("cases/enum.zig");
     _ = @import("cases/enum_with_members.zig");
@@ -48,4 +49,15 @@ comptime {
     _ = @import("cases/var_args.zig");
     _ = @import("cases/void.zig");
     _ = @import("cases/while.zig");
+
+
+    // LLVM 5.0.1, 6.0.0, and trunk crash when attempting to optimize coroutine code.
+    // So, Zig does not support ReleaseFast or ReleaseSafe for coroutines yet.
+    // Luckily, Clang users are running into the same crashes, so folks from the LLVM
+    // community are working on fixes. If we're really lucky they'll be fixed in 6.0.1.
+    // Otherwise we can hope for 7.0.0.
+    if (builtin.mode == builtin.Mode.Debug) {
+        _ = @import("cases/coroutines.zig");
+    }
+
 }
diff --git a/test/cases/coroutines.zig b/test/cases/coroutines.zig
index a20a314c8b..f5e70774fa 100644
--- a/test/cases/coroutines.zig
+++ b/test/cases/coroutines.zig
@@ -4,12 +4,12 @@ const assert = std.debug.assert;
 var x: i32 = 1;
 
 test "create a coroutine and cancel it" {
-    const p = try (async(std.debug.global_allocator) emptyAsyncFn());
+    const p = try (async(std.debug.global_allocator) simpleAsyncFn());
     cancel p;
     assert(x == 2);
 }
 
-async fn emptyAsyncFn() void {
+async fn simpleAsyncFn() void {
     x += 1;
     suspend;
     x += 1;