diff --git a/btest b/btest
index 0d69f77..4dba2ac 100755
--- a/btest
+++ b/btest
@@ -3041,6 +3041,9 @@ def parse_options():
         warning("ignoring requested parallelism in interactive-update mode")
         options.threads = 1
 
+    if options.mode == "UPDATE_INTERACTIVE" and not sys.stdout.isatty():
+        error("interactive-update mode must have a TTY")
+
     return options, parsed_args
 
 
diff --git a/testing/Baseline/tests.update-interactive-requires-tty/output b/testing/Baseline/tests.update-interactive-requires-tty/output
new file mode 100644
index 0000000..d3a6859
--- /dev/null
+++ b/testing/Baseline/tests.update-interactive-requires-tty/output
@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+interactive-update mode must have a TTY
diff --git a/testing/tests/update-interactive-requires-tty.test b/testing/tests/update-interactive-requires-tty.test
new file mode 100644
index 0000000..d716ead
--- /dev/null
+++ b/testing/tests/update-interactive-requires-tty.test
@@ -0,0 +1,8 @@
+# %TEST-DOC: --update-interactive errors out early when stdout is not a TTY.
+#
+# Running btest inside btest redirects the inner stdout, so it is not a
+# TTY and the guard must fire before any test would prompt for input.
+# %TEST-EXEC-FAIL: btest -u . >output 2>&1
+# %TEST-EXEC: btest-diff output
+
+@TEST-EXEC: exit 1