diff --git a/tools/libs/foreignmemory/freebsd.c b/tools/libs/foreignmemory/freebsd.c
index 04bfa806b0..d94ea07862 100644
--- a/tools/libs/foreignmemory/freebsd.c
+++ b/tools/libs/foreignmemory/freebsd.c
@@ -133,9 +133,7 @@ int osdep_xenforeignmemory_map_resource(xenforeignmemory_handle *fmem,
     {
         int saved_errno;
 
-        if ( errno != ENOSYS )
-            ;
-        else
+        if ( errno == ENOSYS )
             errno = EOPNOTSUPP;
 
         if ( fres->addr )
diff --git a/tools/libs/foreignmemory/linux.c b/tools/libs/foreignmemory/linux.c
index 050b9ed3a5..c1f35e2db7 100644
--- a/tools/libs/foreignmemory/linux.c
+++ b/tools/libs/foreignmemory/linux.c
@@ -325,9 +325,7 @@ int osdep_xenforeignmemory_map_resource(
     {
         int saved_errno;
 
-        if ( errno != fmem->unimpl_errno && errno != EOPNOTSUPP )
-            ;
-        else
+        if ( errno == fmem->unimpl_errno )
             errno = EOPNOTSUPP;
 
         if ( fres->addr )
diff --git a/tools/libs/foreignmemory/netbsd.c b/tools/libs/foreignmemory/netbsd.c
index 565682e064..c0b1b8f79d 100644
--- a/tools/libs/foreignmemory/netbsd.c
+++ b/tools/libs/foreignmemory/netbsd.c
@@ -147,6 +147,9 @@ int osdep_xenforeignmemory_map_resource(
     rc = ioctl(fmem->fd, IOCTL_PRIVCMD_MMAP_RESOURCE, &mr);
     if ( rc )
     {
+        if ( errno == ENOSYS )
+            errno = EOPNOTSUPP;
+
         if ( fres->addr )
         {
             int saved_errno = errno;