diff --git a/testing/ostest/sigprocmask.c b/testing/ostest/sigprocmask.c
index f4c8b8fd17..9e12c90774 100644
--- a/testing/ostest/sigprocmask.c
+++ b/testing/ostest/sigprocmask.c
@@ -100,13 +100,19 @@ void sigprocmask_test(void)
     {
       int signo = g_some_signals[i];
 
-      ret = sigaddset(&newmask, signo);
-      if (ret != OK)
+      /* SIGKILL and SIGSTOP should not be added to signal mask */
+
+      if (signo != SIGKILL && signo != SIGSTOP)
         {
-          int errcode = errno;
-          printf("sigprocmask_test: ERROR sigaddset failed: %d\n", errcode);
-          ASSERT(false);
-          goto errout_with_mask;
+          ret = sigaddset(&newmask, signo);
+          if (ret != OK)
+            {
+              int errcode = errno;
+              printf("sigprocmask_test: ERROR sigaddset failed: %d\n",
+                errcode);
+              ASSERT(false);
+              goto errout_with_mask;
+            }
         }
 
       ret = sighold(signo);
@@ -195,6 +201,28 @@ void sigprocmask_test(void)
       goto errout_with_mask;
     }
 
+  /* SIGKILL and SIGSTOP should never be added to signal mask,
+   * so delete them from newmask before comparing.
+   */
+
+  ret = sigdelset(&newmask, SIGKILL);
+  if (ret != OK)
+    {
+      int errcode = errno;
+      printf("sigprocmask_test: ERROR sigprocmask failed: %d\n", errcode);
+      ASSERT(false);
+      goto errout_with_mask;
+    }
+
+  ret = sigdelset(&newmask, SIGSTOP);
+  if (ret != OK)
+    {
+      int errcode = errno;
+      printf("sigprocmask_test: ERROR sigprocmask failed: %d\n", errcode);
+      ASSERT(false);
+      goto errout_with_mask;
+    }
+
   /* It should be the same as newmask */
 
   if (memcmp(&currmask, &newmask, sizeof(sigset_t)) != 0)