diff --git a/backends/json/json.cc b/backends/json/json.cc
index 42eedc606..270d762ee 100644
--- a/backends/json/json.cc
+++ b/backends/json/json.cc
@@ -394,6 +394,7 @@ struct JsonBackend : public Backend {
 		log("      \"bits\": <bit_vector>\n");
 		log("      \"offset\": <the lowest bit index in use, if non-0>\n");
 		log("      \"upto\": <1 if the port bit indexing is MSB-first>\n");
+		log("      \"signed\": <1 if the port is signed>\n");
 		log("    }\n");
 		log("\n");
 		log("The \"offset\" and \"upto\" fields are skipped if their value would be 0.");
@@ -443,6 +444,7 @@ struct JsonBackend : public Backend {
 		log("      \"bits\": <bit_vector>\n");
 		log("      \"offset\": <the lowest bit index in use, if non-0>\n");
 		log("      \"upto\": <1 if the port bit indexing is MSB-first>\n");
+		log("      \"signed\": <1 if the port is signed>\n");
 		log("    }\n");
 		log("\n");
 		log("The \"hide_name\" fields are set to 1 when the name of this cell or net is\n");