diff --git a/src/tools/miri/src/shims/unix/freebsd/foreign_items.rs b/src/tools/miri/src/shims/unix/freebsd/foreign_items.rs
index 70798f98174..d755e5f10ba 100644
--- a/src/tools/miri/src/shims/unix/freebsd/foreign_items.rs
+++ b/src/tools/miri/src/shims/unix/freebsd/foreign_items.rs
@@ -26,8 +26,12 @@ fn emulate_foreign_item_by_name(
             "pthread_set_name_np" => {
                 let [thread, name] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let res =
-                    this.pthread_setname_np(this.read_scalar(thread)?, this.read_scalar(name)?)?;
+                let max_len = usize::MAX; // freebsd does not seem to have a limit.
+                let res = this.pthread_setname_np(
+                    this.read_scalar(thread)?,
+                    this.read_scalar(name)?,
+                    max_len,
+                )?;
                 this.write_scalar(res, dest)?;
             }
 
diff --git a/src/tools/miri/src/shims/unix/linux/foreign_items.rs b/src/tools/miri/src/shims/unix/linux/foreign_items.rs
index c004e2292a9..2b53152688b 100644
--- a/src/tools/miri/src/shims/unix/linux/foreign_items.rs
+++ b/src/tools/miri/src/shims/unix/linux/foreign_items.rs
@@ -68,8 +68,12 @@ fn emulate_foreign_item_by_name(
             "pthread_setname_np" => {
                 let [thread, name] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let res =
-                    this.pthread_setname_np(this.read_scalar(thread)?, this.read_scalar(name)?)?;
+                let max_len = 16;
+                let res = this.pthread_setname_np(
+                    this.read_scalar(thread)?,
+                    this.read_scalar(name)?,
+                    max_len,
+                )?;
                 this.write_scalar(res, dest)?;
             }
             "pthread_getname_np" => {
diff --git a/src/tools/miri/src/shims/unix/macos/foreign_items.rs b/src/tools/miri/src/shims/unix/macos/foreign_items.rs
index 0e931023e6c..371f56ca355 100644
--- a/src/tools/miri/src/shims/unix/macos/foreign_items.rs
+++ b/src/tools/miri/src/shims/unix/macos/foreign_items.rs
@@ -176,7 +176,12 @@ fn emulate_foreign_item_by_name(
             "pthread_setname_np" => {
                 let [name] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                 let thread = this.pthread_self()?;
-                this.pthread_setname_np(thread, this.read_scalar(name)?)?;
+                let max_len = this.eval_libc("MAXTHREADNAMESIZE")?.to_machine_usize(this)?;
+                this.pthread_setname_np(
+                    thread,
+                    this.read_scalar(name)?,
+                    max_len.try_into().unwrap(),
+                )?;
             }
             "pthread_getname_np" => {
                 let [thread, name, len] =
diff --git a/src/tools/miri/src/shims/unix/thread.rs b/src/tools/miri/src/shims/unix/thread.rs
index 4320ecd389e..b43682710bb 100644
--- a/src/tools/miri/src/shims/unix/thread.rs
+++ b/src/tools/miri/src/shims/unix/thread.rs
@@ -67,10 +67,13 @@ fn pthread_self(&mut self) -> InterpResult<'tcx, Scalar<Provenance>> {
         Ok(Scalar::from_machine_usize(thread_id.into(), this))
     }
 
+    /// Set the name of the current thread. `max_name_len` is the maximal length of the name
+    /// including the null terminator.
     fn pthread_setname_np(
         &mut self,
         thread: Scalar<Provenance>,
         name: Scalar<Provenance>,
+        max_name_len: usize,
     ) -> InterpResult<'tcx, Scalar<Provenance>> {
         let this = self.eval_context_mut();
 
@@ -79,8 +82,8 @@ fn pthread_setname_np(
 
         let name = this.read_c_str(name)?.to_owned();
 
-        if name.len() > 15 {
-            // Thread names are limited to 16 characaters, including the null terminator.
+        // Comparing with `>=` to account for null terminator.
+        if name.len() >= max_name_len {
             return this.eval_libc("ERANGE");
         }