$OpenBSD$

Index: runtime/phobos/std/parallelism.d
--- runtime/phobos/std/parallelism.d.orig
+++ runtime/phobos/std/parallelism.d
@@ -99,6 +99,10 @@ else version(FreeBSD)
 {
     version = useSysctlbyname;
 }
+else version(OpenBSD)
+{
+    version = useSysctlbyname;
+}
 else version(DragonFlyBSD)
 {
     version = useSysctlbyname;
@@ -173,6 +177,10 @@ else version(useSysctlbyname)
             auto nameStr = "machdep.cpu.core_count\0".ptr;
         }
         else version(FreeBSD)
+        {
+            auto nameStr = "hw.ncpu\0".ptr;
+        }
+        else version(OpenBSD)
         {
             auto nameStr = "hw.ncpu\0".ptr;
         }
