diff --git a/src/fn_call.rs b/src/fn_call.rs
index 5d41848b643..8909223a31d 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -426,6 +426,7 @@ pub trait EvalContextExt<'a, 'mir, 'tcx: 'a+'mir>: crate::MiriEvalContextExt<'a,
                 let paths = &[
                     (&["libc", "_SC_PAGESIZE"], Scalar::from_int(4096, dest.layout.size)),
                     (&["libc", "_SC_GETPW_R_SIZE_MAX"], Scalar::from_int(-1, dest.layout.size)),
+                    (&["libc", "_SC_NPROCESSORS_ONLN"], Scalar::from_int(1, dest.layout.size)),
                 ];
                 let mut result = None;
                 for &(path, path_value) in paths {
@@ -452,6 +453,10 @@ pub trait EvalContextExt<'a, 'mir, 'tcx: 'a+'mir>: crate::MiriEvalContextExt<'a,
                 }
             }
 
+            "isatty" => {
+                self.write_null(dest)?;
+            }
+
             // Hook pthread calls that go to the thread-local storage memory subsystem
             "pthread_key_create" => {
                 let key_ptr = this.read_scalar(args[0])?.to_ptr()?;