diff --git a/api/client.go b/api/client.go
index 58d203475..86d8d6f02 100644
--- a/api/client.go
+++ b/api/client.go
@@ -320,7 +320,7 @@ func (a *ClientAPI) ElevateClient(ctx *gin.Context) {
 			return
 		}
 
-		elevatedUntil := time.Now().Add(time.Duration(params.DurationSeconds) * time.Second)
+		elevatedUntil := model.ElevationTime(time.Now(), params.DurationSeconds)
 		if err := a.DB.UpdateClientElevatedUntil(client.ID, &elevatedUntil); err != nil {
 			ctx.AbortWithError(500, err)
 			return
diff --git a/api/client_test.go b/api/client_test.go
index b498c1d08..503a1f152 100644
--- a/api/client_test.go
+++ b/api/client_test.go
@@ -358,6 +358,47 @@ func (s *ClientSuite) Test_ElevateClient_expectBadRequestOnMissingDuration() {
 	assert.Nil(s.T(), client.ElevatedUntil)
 }
 
+func (s *ClientSuite) Test_ElevateClient_cancelSuccess() {
+	s.db.User(5).Client(8)
+
+	test.WithUser(s.ctx, 5)
+	elevatedUntil := time.Now().Add(1 * time.Hour)
+	err := s.db.UpdateClientElevatedUntil(8, &elevatedUntil)
+	assert.NoError(s.T(), err)
+	client, err := s.db.GetClientByID(8)
+	assert.NoError(s.T(), err)
+	assert.Equal(s.T(), elevatedUntil.Unix(), client.ElevatedUntil.Unix())
+
+	s.withElevateRequest(8, -1)
+
+	s.a.ElevateClient(s.ctx)
+
+	assert.Equal(s.T(), 204, s.ctx.Writer.Status())
+	client, err = s.db.GetClientByID(8)
+	assert.NoError(s.T(), err)
+	assert.Equal(s.T(), &time.Time{}, client.ElevatedUntil)
+}
+
+func (s *ClientSuite) Test_ElevateClient_clampsHugeDuration() {
+	s.db.User(5).Client(8)
+
+	test.WithUser(s.ctx, 5)
+	// A value that would overflow time.Duration must be clamped to the ceiling
+	// (not rejected, and not wrapped to a past timestamp).
+	s.ctx.AddParam("id", "8")
+	s.withElevateBody(`{"durationSeconds":9223372036854775807}`)
+
+	before := time.Now()
+	s.a.ElevateClient(s.ctx)
+
+	assert.Equal(s.T(), 204, s.ctx.Writer.Status())
+	client, err := s.db.GetClientByID(8)
+	assert.NoError(s.T(), err)
+	assert.NotNil(s.T(), client.ElevatedUntil)
+	// Must be in the future (overflow would have produced a past time).
+	assert.True(s.T(), client.ElevatedUntil.After(before), "elevatedUntil should be in the future, got %v", client.ElevatedUntil)
+}
+
 func (s *ClientSuite) withFormData(formData string) {
 	s.ctx.Request = httptest.NewRequest("POST", "/token", strings.NewReader(formData))
 	s.ctx.Request.Header.Set("Content-Type", "application/x-www-form-urlencoded")
diff --git a/api/oidc.go b/api/oidc.go
index 2e27d2a20..11f02e0f2 100644
--- a/api/oidc.go
+++ b/api/oidc.go
@@ -264,7 +264,7 @@ func (a *OIDCAPI) handleElevationCallback(w http.ResponseWriter, elevate *pendin
 		http.Error(w, "client not found", http.StatusNotFound)
 		return
 	}
-	elevatedUntil := time.Now().Add(time.Duration(elevate.DurationSeconds) * time.Second)
+	elevatedUntil := model.ElevationTime(time.Now(), elevate.DurationSeconds)
 	if err := a.DB.UpdateClientElevatedUntil(client.ID, &elevatedUntil); err != nil {
 		http.Error(w, fmt.Sprintf("failed to elevate session: %v", err), http.StatusInternalServerError)
 		return
diff --git a/model/elevate.go b/model/elevate.go
index f0bd577c7..4887de9b9 100644
--- a/model/elevate.go
+++ b/model/elevate.go
@@ -14,3 +14,21 @@ type ElevateRequest struct {
 }
 
 var DefaultElevationDuration = time.Hour
+
+// maxElevation caps a requested elevation duration (~100 years). A
+// practically "infinite" elevation is intentionally supported, so this is not a
+// security limit; its only purpose is to keep the value well below the point
+// where time.Duration(seconds) * time.Second overflows int64 nanoseconds
+// (~292 years) and would otherwise wrap to a bogus (even past) timestamp.
+const maxElevation = 100 * 365 * 24 * time.Hour
+
+// ElevationTime calculates the time at which an elevation will expire.
+func ElevationTime(base time.Time, deltaSeconds int) time.Time {
+	if deltaSeconds > int(maxElevation/time.Second) {
+		deltaSeconds = int(maxElevation / time.Second)
+	}
+	if deltaSeconds < 0 {
+		return time.Time{}
+	}
+	return base.Add(time.Duration(deltaSeconds) * time.Second)
+}
diff --git a/model/elevate_test.go b/model/elevate_test.go
new file mode 100644
index 000000000..ebb17146e
--- /dev/null
+++ b/model/elevate_test.go
@@ -0,0 +1,52 @@
+package model
+
+import (
+	"math"
+	"testing"
+	"time"
+)
+
+func TestElevationTime(t *testing.T) {
+	// Use runtime variables so arithmetic doesn't happen as a constant
+	// expression and overflow Go's constant checker on either arch.
+	maxInt := math.MaxInt
+	minInt := math.MinInt
+	maxElevationSeconds := int64(maxElevation / time.Second)
+
+	// On 32-bit math.MaxInt (~2.1B) is below maxElevationSeconds (~3.15B),
+	// so no clamp triggers and the expected output is the requested
+	// duration; on 64-bit math.MaxInt is far above, so the expected output
+	// is the cap.
+	var expectedForHuge time.Duration
+	if int64(maxInt) < maxElevationSeconds {
+		expectedForHuge = time.Duration(maxInt) * time.Second
+	} else {
+		expectedForHuge = maxElevation
+	}
+
+	baseTime := time.Now()
+
+	cases := []struct {
+		name    string
+		seconds int
+		want    time.Time
+	}{
+		{"normal", 900, baseTime.Add(900 * time.Second)},
+		{"zero stays zero", 0, baseTime},
+		// Negative values collapse to a one-second past duration so the
+		// client can cancel an elevation (UI sends -1); they must NOT grant
+		// a fresh positive elevation.
+		{"negative value cancels", -1, time.Time{}},
+		{"large negative cancels", minInt, time.Time{}},
+		// A huge positive request is clamped on 64-bit; on 32-bit no clamp
+		// is reachable since math.MaxInt < maxElevationSeconds there.
+		{"huge clamped to max", maxInt, baseTime.Add(expectedForHuge)},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			if got := ElevationTime(baseTime, c.seconds); got != c.want {
+				t.Fatalf("ElevationDuration(%d) = %v, want %v", c.seconds, got, c.want)
+			}
+		})
+	}
+}