diff --git a/net/interfaces/interfaces.go b/net/interfaces/interfaces.go
index 8a45f5673..0682374a0 100644
--- a/net/interfaces/interfaces.go
+++ b/net/interfaces/interfaces.go
@@ -343,6 +343,13 @@ func (s *State) Equal(s2 *State) bool {
 		s.PAC != s2.PAC {
 		return false
 	}
+	// If s2 has more interfaces than s, it's not equal.
+	if len(s.Interface) != len(s2.Interface) || len(s.InterfaceIPs) != len(s2.InterfaceIPs) {
+		return false
+	}
+	// Now that we know that both states have the same number of
+	// interfaces, we can check each interface in s against s2. If it's not
+	// present or not exactly equal, then the states are not equal.
 	for iname, i := range s.Interface {
 		i2, ok := s2.Interface[iname]
 		if !ok {
diff --git a/net/interfaces/interfaces_test.go b/net/interfaces/interfaces_test.go
index 4925600d3..08bfc2b68 100644
--- a/net/interfaces/interfaces_test.go
+++ b/net/interfaces/interfaces_test.go
@@ -286,6 +286,13 @@ func TestStateString(t *testing.T) {
 
 // tests (*State).Equal
 func TestEqual(t *testing.T) {
+	pfxs := func(addrs ...string) (ret []netip.Prefix) {
+		for _, addr := range addrs {
+			ret = append(ret, netip.MustParsePrefix(addr))
+		}
+		return ret
+	}
+
 	tests := []struct {
 		name   string
 		s1, s2 *State
@@ -362,6 +369,29 @@ func TestEqual(t *testing.T) {
 			},
 			want: false,
 		},
+
+		// See tailscale/corp#19124
+		{
+			name: "interface-removed",
+			s1: &State{
+				InterfaceIPs: map[string][]netip.Prefix{
+					"rmnet16":    pfxs("2607:1111:2222:3333:4444:5555:6666:7777/64"),
+					"rmnet17":    pfxs("2607:9999:8888:7777:666:5555:4444:3333/64"),
+					"tun0":       pfxs("100.64.1.2/32", "fd7a:115c:a1e0::1/128"),
+					"v4-rmnet16": pfxs("192.0.0.4/32"),
+					"wlan0":      pfxs("10.0.0.111/24"), // removed below
+				},
+			},
+			s2: &State{
+				InterfaceIPs: map[string][]netip.Prefix{
+					"rmnet16":    pfxs("2607:1111:2222:3333:4444:5555:6666:7777/64"),
+					"rmnet17":    pfxs("2607:9999:8888:7777:666:5555:4444:3333/64"),
+					"tun0":       pfxs("100.64.1.2/32", "fd7a:115c:a1e0::1/128"),
+					"v4-rmnet16": pfxs("192.0.0.4/32"),
+				},
+			},
+			want: false,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {