diff --git a/contrib/libtests/pnggetset.c b/contrib/libtests/pnggetset.c
index e2c1ca556f..f9693172cf 100644
--- a/contrib/libtests/pnggetset.c
+++ b/contrib/libtests/pnggetset.c
@@ -332,6 +332,10 @@ test_text_roundtrip(void)
       text_entries[i].key = (png_charp)keys[i];
       text_entries[i].text = (png_charp)vals[i];
    }
+#ifdef PNG_iTXt_SUPPORTED
+   /* Exercise the documented NULL language pointers for iTXt. */
+   text_entries[TEXT_COUNT - 1].compression = PNG_ITXT_COMPRESSION_NONE;
+#endif
    png_set_text(png_ptr, info_ptr, text_entries, TEXT_COUNT);
 
    /* Get the internal pointer and feed it straight back (append). */
diff --git a/pngset.c b/pngset.c
index 10eea62e54..874fa9baa7 100644
--- a/pngset.c
+++ b/pngset.c
@@ -1105,10 +1105,12 @@ png_set_text_2(const png_struct *png_ptr, png_info *info_ptr,
       if (text_ptr[i].compression > 0)
       {
          textp->lang = textp->key + key_len + 1;
-         memcpy(textp->lang, text_ptr[i].lang, lang_len);
+         if (lang_len != 0)
+            memcpy(textp->lang, text_ptr[i].lang, lang_len);
          *(textp->lang + lang_len) = '\0';
          textp->lang_key = textp->lang + lang_len + 1;
-         memcpy(textp->lang_key, text_ptr[i].lang_key, lang_key_len);
+         if (lang_key_len != 0)
+            memcpy(textp->lang_key, text_ptr[i].lang_key, lang_key_len);
          *(textp->lang_key + lang_key_len) = '\0';
          textp->text = textp->lang_key + lang_key_len + 1;
       }