diff --git a/changelog/unreleased/pull-22163 b/changelog/unreleased/pull-22163
new file mode 100644
index 000000000..af642f111
--- /dev/null
+++ b/changelog/unreleased/pull-22163
@@ -0,0 +1,7 @@
+Bugfix: Report an error for too large numbers in `--keep-within*` durations
+
+Restic crashed with a stack trace when a number in a duration such as the one
+passed to `restic forget --keep-within` did not fit into an integer. It now
+reports an invalid argument instead.
+
+https://github.com/restic/restic/pull/22163
diff --git a/internal/data/duration.go b/internal/data/duration.go
index 9762b70e6..d912f3007 100644
--- a/internal/data/duration.go
+++ b/internal/data/duration.go
@@ -65,7 +65,7 @@ func nextNumber(input string) (num int, rest string, err error) {
 
 	num, err = strconv.Atoi(n)
 	if err != nil {
-		panic(err)
+		return 0, input, err
 	}
 
 	if negative {
diff --git a/internal/data/duration_test.go b/internal/data/duration_test.go
index bd421bd91..15cb8b328 100644
--- a/internal/data/duration_test.go
+++ b/internal/data/duration_test.go
@@ -40,6 +40,9 @@ func TestNextNumber(t *testing.T) {
 		{
 			input: "5", num: 5, rest: "",
 		},
+		{
+			input: "99999999999999999999999999y", num: 0, rest: "99999999999999999999999999y", err: true,
+		},
 	}
 
 	for _, test := range tests {
@@ -82,6 +85,8 @@ func TestParseDuration(t *testing.T) {
 		{input: "1y4m3w1d", err: true},
 		{input: "s", err: true},
 		{input: "\xdf\x80", err: true}, // NKO DIGIT ZERO; we want ASCII digits
+		{input: "99999999999999999999999999y", err: true},
+		{input: "1y-99999999999999999999999999d", err: true},
 	}
 
 	for _, test := range tests {