diff --git a/tools/libxc/xc_freebsd_osdep.c b/tools/libxc/xc_freebsd_osdep.c
index 151d3bfc57..e6613ef00a 100644
--- a/tools/libxc/xc_freebsd_osdep.c
+++ b/tools/libxc/xc_freebsd_osdep.c
@@ -125,10 +125,13 @@ static void freebsd_privcmd_free_hypercall_buffer(xc_interface *xch,
                                                   int npages)
 {
 
+    int saved_errno = errno;
     /* Unlock pages */
     munlock(ptr, npages * XC_PAGE_SIZE);
 
     munmap(ptr, npages * XC_PAGE_SIZE);
+    /* We MUST propagate the hypercall errno, not unmap call's. */
+    errno = saved_errno;
 }
 
 static int freebsd_privcmd_hypercall(xc_interface *xch, xc_osdep_handle h,
diff --git a/tools/libxc/xc_hcall_buf.c b/tools/libxc/xc_hcall_buf.c
index e762a93a67..932b47c2ef 100644
--- a/tools/libxc/xc_hcall_buf.c
+++ b/tools/libxc/xc_hcall_buf.c
@@ -33,16 +33,22 @@ pthread_mutex_t hypercall_buffer_cache_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 static void hypercall_buffer_cache_lock(xc_interface *xch)
 {
+    int saved_errno = errno;
     if ( xch->flags & XC_OPENFLAG_NON_REENTRANT )
         return;
     pthread_mutex_lock(&hypercall_buffer_cache_mutex);
+    /* Ignore pthread errors. */
+    errno = saved_errno;
 }
 
 static void hypercall_buffer_cache_unlock(xc_interface *xch)
 {
+    int saved_errno = errno;
     if ( xch->flags & XC_OPENFLAG_NON_REENTRANT )
         return;
     pthread_mutex_unlock(&hypercall_buffer_cache_mutex);
+    /* Ignore pthread errors. */
+    errno = saved_errno;
 }
 
 static void *hypercall_buffer_cache_alloc(xc_interface *xch, int nr_pages)
diff --git a/tools/libxc/xc_linux_osdep.c b/tools/libxc/xc_linux_osdep.c
index 92f7cace97..2687424305 100644
--- a/tools/libxc/xc_linux_osdep.c
+++ b/tools/libxc/xc_linux_osdep.c
@@ -122,10 +122,13 @@ out:
 
 static void linux_privcmd_free_hypercall_buffer(xc_interface *xch, xc_osdep_handle h, void *ptr, int npages)
 {
+    int saved_errno = errno;
     /* Recover the VMA flags. Maybe it's not necessary */
     madvise(ptr, npages * XC_PAGE_SIZE, MADV_DOFORK);
 
     munmap(ptr, npages * XC_PAGE_SIZE);
+    /* We MUST propagate the hypercall errno, not unmap call's. */
+    errno = saved_errno;
 }
 
 static int linux_privcmd_hypercall(xc_interface *xch, xc_osdep_handle h, privcmd_hypercall_t *hypercall)