diff --git a/src/json.c b/src/json.c
index adc491e..636f174 100644
--- a/src/json.c
+++ b/src/json.c
@@ -93,8 +93,8 @@ write_iov (
     while (1) {
         ssize_t nbytes = writev(fd, bufv, bufcnt);
         if (unlikely(nbytes < 0)) {
-            int err = errno;
-            log_printf("writev(): %s", xstrerror(err));
+            int err;
+            log_printf("writev(): %s", xstrerror_save(&err));
 
             switch (err) {
               case EIO:
diff --git a/src/xstd.c b/src/xstd.c
index ee2b7b0..dc770d7 100644
--- a/src/xstd.c
+++ b/src/xstd.c
@@ -66,8 +66,8 @@ xfsync (
     int fd
 ) {
     while (unlikely(0 != fsync(fd))) {
-        int err = errno;
-        log_printf("fsync(): %s", xstrerror(err));
+        int err;
+        log_printf("fsync(): %s", xstrerror_save(&err));
 
         switch (err) {
           case EIO:
@@ -170,3 +170,13 @@ xstrerror (
     }
     return err_str;
 }
+
+char const *
+xstrerror_save (
+    int *errnum_ptr
+) {
+    int err = errno;
+
+    *errnum_ptr = err;
+    return xstrerror(err);
+}
diff --git a/src/xstd.h b/src/xstd.h
index 9720be3..0320d7d 100644
--- a/src/xstd.h
+++ b/src/xstd.h
@@ -169,4 +169,15 @@ xstrerror (
     int errnum
 );
 
+/**
+ * Like xstrerror(), but takes `errno` as error number,
+ * and saves its value to `err_ptr`.
+ */
+BOOKMARKFS_INTERNAL
+FUNCATTR_RETURNS_NONNULL
+char const *
+xstrerror_save (
+    int *errnum_ptr
+);
+
 #endif  /* !defined(BOOKMARKFS_XSTD_H_) */