diff --git a/certificates.go b/certificates.go
index f92d9b8f..e7cfa5fe 100644
--- a/certificates.go
+++ b/certificates.go
@@ -651,6 +651,11 @@ func isInternalIP(addr string) bool {
 func hostOnly(hostport string) string {
 	host, _, err := net.SplitHostPort(hostport)
 	if err != nil {
+		// May be a bare IPv6 address in brackets without a port (e.g. "[::1]").
+		// net.SplitHostPort requires a port when brackets are present, so strip them.
+		if len(hostport) > 1 && hostport[0] == '[' && hostport[len(hostport)-1] == ']' {
+			return hostport[1 : len(hostport)-1]
+		}
 		return hostport // OK; probably had no port to begin with
 	}
 	return host
@@ -665,6 +670,8 @@ func hostOnly(hostport string) string {
 // It uses DNS wildcard matching logic and is case-insensitive.
 // https://tools.ietf.org/html/rfc2818#section-3.1
 func MatchWildcard(subject, wildcard string) bool {
+	// Strip brackets from IPv6 addresses (e.g. "[::1]" from HTTP Host headers).
+	subject = hostOnly(subject)
 	subject, wildcard = strings.ToLower(subject), strings.ToLower(wildcard)
 	if subject == wildcard {
 		return true
diff --git a/certificates_test.go b/certificates_test.go
index f8ecc3df..a53abcb5 100644
--- a/certificates_test.go
+++ b/certificates_test.go
@@ -189,6 +189,37 @@ func TestSubjectQualifiesForPublicCert(t *testing.T) {
 	}
 }
 
+func TestHostOnly(t *testing.T) {
+	for i, test := range []struct {
+		input  string
+		expect string
+	}{
+		// hostname without port
+		{"example.com", "example.com"},
+		// hostname with port
+		{"example.com:443", "example.com"},
+		// IPv4 without port
+		{"1.2.3.4", "1.2.3.4"},
+		// IPv4 with port
+		{"1.2.3.4:80", "1.2.3.4"},
+		// IPv6 without port and without brackets
+		{"::1", "::1"},
+		// IPv6 with port (brackets required by RFC 7230)
+		{"[::1]:80", "::1"},
+		// IPv6 without port but with brackets (Go's HTTP server format for host-only)
+		{"[::1]", "::1"},
+		// full IPv6 without port but with brackets
+		{"[2001:db8::1]", "2001:db8::1"},
+		// full IPv6 with port
+		{"[2001:db8::1]:8080", "2001:db8::1"},
+	} {
+		actual := hostOnly(test.input)
+		if actual != test.expect {
+			t.Errorf("Test %d: hostOnly(%q) = %q, want %q", i, test.input, actual, test.expect)
+		}
+	}
+}
+
 func TestMatchWildcard(t *testing.T) {
 	for i, test := range []struct {
 		subject, wildcard string
@@ -217,6 +248,10 @@ func TestMatchWildcard(t *testing.T) {
 		{"1.2.3.4.5.6", "*.*.*.*.*.*", true},
 		{"0.1.2.3.4.5.6", "*.*.*.*.*.*", false},
 		{"1.2.3.4", "1.2.3.*", false}, // https://tools.ietf.org/html/rfc2818#section-3.1
+		// Bracketed IPv6 subjects (from HTTP Host headers) must match bare IPv6 wildcards.
+		{"[::1]", "::1", true},
+		{"[2001:db8::1]", "2001:db8::1", true},
+		{"[::1]", "::2", false},
 	} {
 		actual := MatchWildcard(test.subject, test.wildcard)
 		if actual != test.expect {
diff --git a/solvers.go b/solvers.go
index 677fad3f..b4801303 100644
--- a/solvers.go
+++ b/solvers.go
@@ -768,6 +768,8 @@ func dialTCPSocket(addr string) error {
 // GetACMEChallenge returns an active ACME challenge for the given identifier,
 // or false if no active challenge for that identifier is known.
 func GetACMEChallenge(identifier string) (Challenge, bool) {
+	// Strip brackets from IPv6 addresses (e.g. "[::1]" from HTTP Host headers).
+	identifier = hostOnly(identifier)
 	activeChallengesMu.Lock()
 	chalData, ok := activeChallenges[identifier]
 	activeChallengesMu.Unlock()
diff --git a/solvers_test.go b/solvers_test.go
index d30ce66d..c9fc1974 100644
--- a/solvers_test.go
+++ b/solvers_test.go
@@ -155,3 +155,25 @@ func Test_challengeKey(t *testing.T) {
 		})
 	}
 }
+
+func TestGetACMEChallenge_IPv6Brackets(t *testing.T) {
+	// Store a challenge under a bare IPv6 identifier (as CertMagic does internally).
+	bare := "::1"
+	activeChallengesMu.Lock()
+	activeChallenges[bare] = Challenge{}
+	activeChallengesMu.Unlock()
+	defer func() {
+		activeChallengesMu.Lock()
+		delete(activeChallenges, bare)
+		activeChallengesMu.Unlock()
+	}()
+
+	// Lookup with bracketed IPv6 (as received from Go's HTTP server via r.Host).
+	if _, ok := GetACMEChallenge("[::1]"); !ok {
+		t.Error("GetACMEChallenge(\"[::1]\") should find challenge stored under \"::1\"")
+	}
+	// Lookup with bare IPv6 should still work.
+	if _, ok := GetACMEChallenge("::1"); !ok {
+		t.Error("GetACMEChallenge(\"::1\") should find challenge stored under \"::1\"")
+	}
+}