diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index ea60f6055f3d5..9657e2af3e6d0 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -255,8 +255,11 @@ impl ModuleConfig {
             {
                 MergeFunctions::Disabled => false,
                 MergeFunctions::Trampolines | MergeFunctions::Aliases => {
-                    sess.opts.optimize == config::OptLevel::Default
-                        || sess.opts.optimize == config::OptLevel::Aggressive
+                    use config::OptLevel::*;
+                    match sess.opts.optimize {
+                        Aggressive | Default | SizeMin | Size => true,
+                        Less | No => false,
+                    }
                 }
             },
 
diff --git a/src/test/codegen/merge-functions.rs b/src/test/codegen/merge-functions.rs
index 5eefc0f98f1fe..d6caeeee89669 100644
--- a/src/test/codegen/merge-functions.rs
+++ b/src/test/codegen/merge-functions.rs
@@ -1,7 +1,9 @@
-// compile-flags: -O
+// revisions: O Os
+//[Os] compile-flags: -Copt-level=s
+//[O] compile-flags: -O
 #![crate_type = "lib"]
 
-// CHECK: @func2 = {{.*}}alias{{.*}}@func1
+// CHECK: @func{{2|1}} = {{.*}}alias{{.*}}@func{{1|2}}
 
 #[no_mangle]
 pub fn func1(c: char) -> bool {