diff --git a/MANIFEST b/MANIFEST
index e7351c6..c43d26a 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -16,6 +16,7 @@ t/fakelib/Crypt/OpenSSL/Bignum.pm
 t/format.t
 t/key_lifecycle.t
 t/padding.t
+t/pkcs1_sign.t
 t/private_crypt.t
 t/pss_auto_promote.t
 t/rsa.t
diff --git a/t/pkcs1_sign.t b/t/pkcs1_sign.t
new file mode 100644
index 0000000..4032a62
--- /dev/null
+++ b/t/pkcs1_sign.t
@@ -0,0 +1,104 @@
+use strict;
+use Test::More;
+
+use Crypt::OpenSSL::Random;
+use Crypt::OpenSSL::RSA;
+
+use Crypt::OpenSSL::Guess qw(openssl_version);
+
+my ($major, $minor, $patch) = openssl_version();
+
+# Regression tests for PKCS#1 v1.5 signing (RSASSA-PKCS1-v1_5).
+# Issue #146: PKCS#1 v1.5 was disabled entirely in v0.35 to mitigate
+# the Marvin attack, but the Marvin attack only affects decryption.
+# PKCS#1 v1.5 signatures are secure and required by protocols like
+# ACME/Let's Encrypt (RS256) and many JOSE/JWS implementations.
+
+plan tests => 10;
+
+Crypt::OpenSSL::Random::random_seed("OpenSSL needs at least 32 bytes.");
+Crypt::OpenSSL::RSA->import_random_seed();
+
+my $rsa = Crypt::OpenSSL::RSA->generate_key(2048);
+my $pub_pem = $rsa->get_public_key_x509_string();
+my $rsa_pub = Crypt::OpenSSL::RSA->new_public_key($pub_pem);
+
+# --- use_pkcs1_padding() must not croak ---
+eval { $rsa->use_pkcs1_padding() };
+ok(!$@, "use_pkcs1_padding() does not croak");
+
+# --- SHA-256 sign/verify (RS256 — used by ACME/Let's Encrypt) ---
+{
+    $rsa->use_pkcs1_padding();
+    $rsa->use_sha256_hash();
+    $rsa_pub->use_pkcs1_padding();
+    $rsa_pub->use_sha256_hash();
+
+    my $msg = '{"protected":"...","payload":"..."}';
+    my $sig = $rsa->sign($msg);
+    ok(defined $sig && length($sig) > 0,
+       "PKCS#1 v1.5 + SHA-256 sign produces signature");
+
+    ok($rsa_pub->verify($msg, $sig),
+       "PKCS#1 v1.5 + SHA-256 signature verifies");
+
+    ok(!$rsa_pub->verify("tampered", $sig),
+       "PKCS#1 v1.5 + SHA-256 rejects tampered message");
+}
+
+# --- SHA-1 sign/verify (RS1 — legacy but still used) ---
+SKIP: {
+    $rsa->use_pkcs1_padding();
+    $rsa->use_sha1_hash();
+    my $sig = eval { $rsa->sign("sha1 test") };
+    skip "SHA-1 signing not available on this system", 2 if $@;
+
+    ok(defined $sig, "PKCS#1 v1.5 + SHA-1 sign produces signature");
+
+    $rsa_pub->use_pkcs1_padding();
+    $rsa_pub->use_sha1_hash();
+    ok($rsa_pub->verify("sha1 test", $sig),
+       "PKCS#1 v1.5 + SHA-1 signature verifies");
+}
+
+# --- Cross-padding: sign with PKCS1, verify with PSS must fail ---
+SKIP: {
+    skip "sign uses pkcs1_padding only on OpenSSL < 3.x", 1
+        if $major < 3;
+    $rsa->use_pkcs1_padding();
+    $rsa->use_sha256_hash();
+    my $sig = $rsa->sign("cross-padding test");
+
+    $rsa_pub->use_pkcs1_pss_padding();
+    $rsa_pub->use_sha256_hash();
+    my $result = eval { $rsa_pub->verify("cross-padding test", $sig) };
+    ok(!$result, "PKCS1 signature does not verify with PSS padding");
+}
+
+# --- Encryption with PKCS1 must still croak (Marvin protection) ---
+{
+    $rsa->use_pkcs1_padding();
+    eval { $rsa->encrypt("test") };
+    like($@, qr/Marvin|vulnerable/i,
+         "PKCS#1 v1.5 encryption still blocked (Marvin)");
+}
+
+# --- Reload key from PEM and verify signature ---
+{
+    $rsa->use_pkcs1_padding();
+    $rsa->use_sha256_hash();
+    my $sig = $rsa->sign("persistence test");
+
+    my $priv_pem = $rsa->get_private_key_string();
+    my $rsa2 = Crypt::OpenSSL::RSA->new_private_key($priv_pem);
+    $rsa2->use_pkcs1_padding();
+    $rsa2->use_sha256_hash();
+    ok($rsa2->verify("persistence test", $sig),
+       "signature verifies after key round-trip through PEM");
+
+    my $rsa_pub2 = Crypt::OpenSSL::RSA->new_public_key($pub_pem);
+    $rsa_pub2->use_pkcs1_padding();
+    $rsa_pub2->use_sha256_hash();
+    ok($rsa_pub2->verify("persistence test", $sig),
+       "signature verifies with fresh public key object");
+}