diff --git a/src/shims/foreign_items/posix.rs b/src/shims/foreign_items/posix.rs
index db2fab526c1..1652a3a1b54 100644
--- a/src/shims/foreign_items/posix.rs
+++ b/src/shims/foreign_items/posix.rs
@@ -335,16 +335,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let result = this.pthread_condattr_init(attr)?;
                 this.write_scalar(Scalar::from_i32(result), dest)?;
             }
-            "pthread_condattr_setclock" => {
-                let &[attr, clock_id] = check_arg_count(args)?;
-                let result = this.pthread_condattr_setclock(attr, clock_id)?;
-                this.write_scalar(Scalar::from_i32(result), dest)?;
-            }
-            "pthread_condattr_getclock" => {
-                let &[attr, clock_id] = check_arg_count(args)?;
-                let result = this.pthread_condattr_getclock(attr, clock_id)?;
-                this.write_scalar(Scalar::from_i32(result), dest)?;
-            }
             "pthread_condattr_destroy" => {
                 let &[attr] = check_arg_count(args)?;
                 let result = this.pthread_condattr_destroy(attr)?;
diff --git a/src/shims/foreign_items/posix/linux.rs b/src/shims/foreign_items/posix/linux.rs
index e0f54cac157..323418f39ba 100644
--- a/src/shims/foreign_items/posix/linux.rs
+++ b/src/shims/foreign_items/posix/linux.rs
@@ -90,6 +90,16 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let result = this.prctl(option, arg2, arg3, arg4, arg5)?;
                 this.write_scalar(Scalar::from_i32(result), dest)?;
             }
+            "pthread_condattr_setclock" => {
+                let &[attr, clock_id] = check_arg_count(args)?;
+                let result = this.pthread_condattr_setclock(attr, clock_id)?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
+            }
+            "pthread_condattr_getclock" => {
+                let &[attr, clock_id] = check_arg_count(args)?;
+                let result = this.pthread_condattr_getclock(attr, clock_id)?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
+            }
 
             // Dynamically invoked syscalls
             "syscall" => {
diff --git a/src/sync.rs b/src/sync.rs
index 026542926ed..107ad5ace17 100644
--- a/src/sync.rs
+++ b/src/sync.rs
@@ -238,6 +238,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         match this.machine.threads.sync.rwlocks[id].readers.entry(reader) {
             Entry::Occupied(mut entry) => {
                 let count = entry.get_mut();
+                assert!(*count > 0, "rwlock locked with count == 0");
                 *count -= 1;
                 if *count == 0 {
                     entry.remove();