diff --git a/src/lib.rs b/src/lib.rs
index 4c51fac..f4bbb65 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -177,11 +177,24 @@ psm_stack_manipulation! {
                     old_stack_limit: get_stack_limit(),
                 };
                 let above_guard_page = new_stack.add(page_size);
+                #[cfg(not(target_os = "openbsd"))]
                 let result = libc::mprotect(
                     above_guard_page,
                     stack_bytes - page_size,
                     libc::PROT_READ | libc::PROT_WRITE
                 );
+                #[cfg(target_os = "openbsd")]
+                let result = if libc::mmap(
+                        above_guard_page,
+                        stack_bytes - page_size,
+                        libc::PROT_READ | libc::PROT_WRITE,
+                        libc::MAP_FIXED | libc::MAP_PRIVATE | libc::MAP_ANON | libc::MAP_STACK,
+                        -1,
+                        0) == above_guard_page {
+                    0
+                } else {
+                    -1
+                };
                 if result == -1 {
                     drop(guard);
                     panic!("unable to set stack permissions")
@@ -372,8 +385,8 @@ cfg_if! {
     } else if #[cfg(target_os = "openbsd")] {
         unsafe fn guess_os_stack_limit() -> Option<usize> {
             let mut stackinfo = std::mem::MaybeUninit::<libc::stack_t>::uninit();
-            assert_eq!(libc::pthread_stackseg_np(libc::pthread_self(), stackinfo.as_mut_ptr()));
-            Some(stackinfo.assume_init().ss_sp)
+            assert_eq!(libc::pthread_stackseg_np(libc::pthread_self(), stackinfo.as_mut_ptr()), 0);
+            Some(stackinfo.assume_init().ss_sp as usize - stackinfo.assume_init().ss_size)
         }
     } else if #[cfg(target_os = "macos")] {
         unsafe fn guess_os_stack_limit() -> Option<usize> {