diff --git a/core/objects.go b/core/objects.go
index ad09b01611b..443e1a693da 100644
--- a/core/objects.go
+++ b/core/objects.go
@@ -456,6 +456,7 @@ func (window SuggestedWindow) IsWithin(now time.Time) bool {
 // endpoint specified in draft-aaron-ari.
 type RenewalInfo struct {
 	SuggestedWindow SuggestedWindow `json:"suggestedWindow"`
+	ExplanationURL  string          `json:"explanationURL,omitempty"`
 }
 
 // RenewalInfoSimple constructs a `RenewalInfo` object and suggested window
@@ -478,13 +479,15 @@ func RenewalInfoSimple(issued time.Time, expires time.Time) RenewalInfo {
 // window in the past. Per the draft-ietf-acme-ari-01 spec, clients should
 // attempt to renew immediately if the suggested window is in the past. The
 // passed `now` is assumed to be a timestamp representing the current moment in
-// time.
-func RenewalInfoImmediate(now time.Time) RenewalInfo {
+// time. The `explanationURL` is an optional URL that the subscriber can use to
+// learn more about why the renewal is suggested.
+func RenewalInfoImmediate(now time.Time, explanationURL string) RenewalInfo {
 	oneHourAgo := now.Add(-1 * time.Hour)
 	return RenewalInfo{
 		SuggestedWindow: SuggestedWindow{
 			Start: oneHourAgo,
 			End:   oneHourAgo.Add(time.Minute * 30),
 		},
+		ExplanationURL: explanationURL,
 	}
 }
diff --git a/wfe2/wfe.go b/wfe2/wfe.go
index 11e3fcf58cb..22526275ed9 100644
--- a/wfe2/wfe.go
+++ b/wfe2/wfe.go
@@ -2118,8 +2118,15 @@ func (wfe *WebFrontEndImpl) determineARIWindow(ctx context.Context, serial strin
 	}
 
 	if len(result.Incidents) > 0 {
+		// Find the earliest incident.
+		var earliest *sapb.Incident
+		for _, incident := range result.Incidents {
+			if earliest == nil || incident.RenewBy.AsTime().Before(earliest.RenewBy.AsTime()) {
+				earliest = incident
+			}
+		}
 		// The existing cert is impacted by an incident, renew immediately.
-		return core.RenewalInfoImmediate(wfe.clk.Now()), nil
+		return core.RenewalInfoImmediate(wfe.clk.Now(), earliest.Url), nil
 	}
 
 	// Check if the serial is revoked.
@@ -2130,7 +2137,7 @@ func (wfe *WebFrontEndImpl) determineARIWindow(ctx context.Context, serial strin
 
 	if status.Status == string(core.OCSPStatusRevoked) {
 		// The existing certificate is revoked, renew immediately.
-		return core.RenewalInfoImmediate(wfe.clk.Now()), nil
+		return core.RenewalInfoImmediate(wfe.clk.Now(), ""), nil
 	}
 
 	// It's okay to use GetCertificate (vs trying to get a precertificate),
diff --git a/wfe2/wfe_test.go b/wfe2/wfe_test.go
index 7f2afaa5aa6..19c7cc8ac11 100644
--- a/wfe2/wfe_test.go
+++ b/wfe2/wfe_test.go
@@ -1920,7 +1920,7 @@ func newMockSAWithIncident(sa sapb.StorageAuthorityReadOnlyClient, serial []stri
 				{
 					Id:          0,
 					SerialTable: "incident_foo",
-					Url:         agreementURL,
+					Url:         "http://big.bad/incident",
 					RenewBy:     nil,
 					Enabled:     true,
 				},
@@ -3785,6 +3785,8 @@ func TestIncidentARI(t *testing.T) {
 	test.AssertEquals(t, ri.SuggestedWindow.End.After(ri.SuggestedWindow.Start), true)
 	// The end of the window should also be in the past.
 	test.AssertEquals(t, ri.SuggestedWindow.End.Before(wfe.clk.Now()), true)
+	// The explanationURL should be set.
+	test.AssertEquals(t, ri.ExplanationURL, "http://big.bad/incident")
 }
 
 func TestOldTLSInbound(t *testing.T) {