diff --git a/mockall/tests/automock_foreign_c.rs b/mockall/tests/automock_foreign_c.rs
index 864bc77f..ce4a98e3 100644
--- a/mockall/tests/automock_foreign_c.rs
+++ b/mockall/tests/automock_foreign_c.rs
@@ -7,46 +7,47 @@ use std::sync::Mutex;
 #[automock]
 mod ffi {
     extern "C" {
-        pub(super) fn foo(x: u32) -> i64;
+        // This is provided by the C library
+        pub(super) fn isupper(c: i32) -> i32;
     }
 }
 
-static FOO_MTX: Mutex<()> = Mutex::new(());
+static ISUPPER_MTX: Mutex<()> = Mutex::new(());
 
 // Ensure we can still use the original mocked function
+#[test]
 pub fn normal_usage() {
-    let _m = FOO_MTX.lock();
-    unsafe {
-        ffi::foo(42);
-    }
+    let _m = ISUPPER_MTX.lock();
+    assert!(0 != unsafe { ffi::isupper('A' as i32)});    // 'A'
+    assert_eq!(0, !unsafe { ffi::isupper('a' as i32)});   // 'a'
 }
 
 #[test]
-#[should_panic(expected = "mock_ffi::foo(5): No matching expectation found")]
+#[should_panic(expected = "mock_ffi::isupper(5): No matching expectation found")]
 fn with_no_matches() {
-    let _m = FOO_MTX.lock();
-    let ctx = mock_ffi::foo_context();
+    let _m = ISUPPER_MTX.lock();
+    let ctx = mock_ffi::isupper_context();
     ctx.expect()
         .with(predicate::eq(4))
-        .returning(i64::from);
-    unsafe{ mock_ffi::foo(5) };
+        .returning(i32::from);
+    unsafe{ mock_ffi::isupper(5) };
 }
 
 #[test]
 fn returning() {
-    let _m = FOO_MTX.lock();
-    let ctx = mock_ffi::foo_context();
-    ctx.expect().returning(i64::from);
-    assert_eq!(42, unsafe{mock_ffi::foo(42)});
+    let _m = ISUPPER_MTX.lock();
+    let ctx = mock_ffi::isupper_context();
+    ctx.expect().returning(i32::from);
+    assert_eq!(42, unsafe{mock_ffi::isupper(42)});
 }
 
 /// Ensure that the mock function can be called from C by casting it to a C
 /// function pointer.
 #[test]
 fn c_abi() {
-    let _m = FOO_MTX.lock();
-    let ctx = mock_ffi::foo_context();
-    ctx.expect().returning(i64::from);
-    let p: unsafe extern "C-unwind" fn(u32) -> i64 = mock_ffi::foo;
+    let _m = ISUPPER_MTX.lock();
+    let ctx = mock_ffi::isupper_context();
+    ctx.expect().returning(i32::from);
+    let p: unsafe extern "C-unwind" fn(i32) -> i32 = mock_ffi::isupper;
     assert_eq!(42, unsafe{p(42)});
 }