diff --git a/src/lua/error.lua b/src/lua/error.lua
index 5adf83c5e8..130943751d 100644
--- a/src/lua/error.lua
+++ b/src/lua/error.lua
@@ -269,6 +269,7 @@ local function error_to_string(err)
     end
 
     local ibuf = buffer.internal.cord_ibuf_take()
+    ibuf:reserve(ibuf:capacity())
     local len = ffi.C.error_to_string(err, ibuf.wpos, ibuf:capacity())
     if len + 1 > ibuf:capacity() then
         ibuf:reserve(len + 1)
diff --git a/test/unit/error.c b/test/unit/error.c
index 44a90f6a1c..e597873144 100644
--- a/test/unit/error.c
+++ b/test/unit/error.c
@@ -672,15 +672,18 @@ test_logging(void)
 
 	/* Some of basic errors. */
 	e = BuildTimedOut("filename", 303);
+	error_ref(e);
 	error_log(e);
 	fail_unless(fgets(buf, size, f) != NULL);
 	ok(strstr(buf,
 		  "E> timed out "
 		  "{\"type\":\"TimedOut\",\"errno\":110,"
 		  "\"trace\":[{\"file\":\"filename\",\"line\":303}]}") != NULL);
+	error_unref(e);
 
 	/* ClientError plus payload plus some escaping. */
 	e = BuildClientError("\"filename\"", 707, ER_READONLY);
+	error_ref(e);
 	/* Check json escaping payload name and data. */
 	error_set_str(e, "\"f1\"", "\"p1\"");
 	error_log(e);
@@ -692,13 +695,15 @@ test_logging(void)
 		  "\"\\\"f1\\\"\":\"\\\"p1\\\"\","
 		  "\"trace\":[{\"file\":\"\\\"filename\\\"\",\"line\":707}]}"
 		  ) != NULL);
+	error_unref(e);
 
 	/* CustomError plus some unusual branches. */
 	/* 1. Check json escaping custom type. */
 	/* 2. Check no trace. */
 	/* 3. Check zero code. */
 	e = BuildCustomError("", 505, "\"typo\"", 0);
-	e->errmsg = "some message";
+	error_ref(e);
+	strcpy(e->errmsg_buf, "some message");
 	/* 4. Check errno. */
 	e->saved_errno = 11;
 	error_log(e);
@@ -707,14 +712,16 @@ test_logging(void)
 		  "E> some message "
 		  "{\"type\":\"\\\"typo\\\"\",\"errno\":11,"
 		  "\"trace\":[{}]}") != NULL);
+	error_unref(e);
 
 	/* Check stacked error. */
 	struct error *e1 = BuildCustomError("", 101, "level_1", 0);
-	e1->errmsg = "message 1";
+	error_ref(e1);
+	strcpy(e1->errmsg_buf, "message 1");
 	struct error *e2 = BuildCustomError("", 202, "level_2", 0);
-	e2->errmsg = "message 2";
+	strcpy(e2->errmsg_buf, "message 2");
 	struct error *e3 = BuildCustomError("", 303, "level_3", 0);
-	e3->errmsg = "message 3";
+	strcpy(e3->errmsg_buf, "message 3");
 	error_set_prev(e1, e2);
 	error_set_prev(e2, e3);
 	error_log(e2);
@@ -728,6 +735,7 @@ test_logging(void)
 		  "Caused by: message 3 "
 		  "{\"type\":\"level_3\","
 		  "\"trace\":[{}]}") != 0);
+	error_unref(e1);
 
 	fclose(f);
 	say_logger_free();