diff --git a/lib/HTTP/Tiny.pm b/lib/HTTP/Tiny.pm
index fbbe00b..06d4152 100644
--- a/lib/HTTP/Tiny.pm
+++ b/lib/HTTP/Tiny.pm
@@ -1178,12 +1178,14 @@ sub start_ssl {
     }
 
     my $ssl_args = $self->_ssl_args($host);
+    my $user_cb  = $ssl_args->{SSL_create_ctx_callback};
     IO::Socket::SSL->start_SSL(
         $self->{fh},
         %$ssl_args,
         SSL_create_ctx_callback => sub {
             my $ctx = shift;
             Net::SSLeay::CTX_set_mode($ctx, Net::SSLeay::MODE_AUTO_RETRY());
+            $user_cb->($ctx) if $user_cb;
         },
     );
 
diff --git a/t/185_ssl_ctx_callback.t b/t/185_ssl_ctx_callback.t
new file mode 100644
index 0000000..03e532b
--- /dev/null
+++ b/t/185_ssl_ctx_callback.t
@@ -0,0 +1,111 @@
+#!perl
+
+use strict;
+use warnings;
+
+use Test::More 0.88;
+
+plan skip_all => "IO::Socket::SSL required for SSL tests"
+  unless eval { require IO::Socket::SSL; 1 };
+
+plan skip_all => "Net::SSLeay required for SSL tests"
+  unless eval { require Net::SSLeay; 1 };
+
+use HTTP::Tiny;
+
+# Test that a user-provided SSL_create_ctx_callback in SSL_options is not
+# silently overwritten but instead composed with the internal MODE_AUTO_RETRY
+# callback. See https://github.com/Perl-Toolchain-Gang/HTTP-Tiny/issues/19
+
+# Test 1: _ssl_args preserves the user's SSL_create_ctx_callback
+{
+    my $user_cb = sub { 'user' };
+
+    my $h = bless {
+        SSL_options => { SSL_create_ctx_callback => $user_cb },
+        verify_SSL  => 0,
+    }, 'HTTP::Tiny::Handle';
+
+    my $ssl_args = $h->_ssl_args('example.com');
+
+    is( ref($ssl_args->{SSL_create_ctx_callback}), 'CODE',
+        '_ssl_args preserves SSL_create_ctx_callback as CODE ref' );
+
+    is( $ssl_args->{SSL_create_ctx_callback}, $user_cb,
+        '_ssl_args preserves the exact user callback reference' );
+}
+
+# Test 2: start_ssl composes the user callback with the internal MODE_AUTO_RETRY callback
+{
+    my $mode_auto_retry_called = 0;
+    my $user_cb_called         = 0;
+    my $user_cb = sub { $user_cb_called++ };
+
+    no warnings 'redefine';
+    local *Net::SSLeay::CTX_set_mode  = sub { $mode_auto_retry_called++ };
+    local *Net::SSLeay::MODE_AUTO_RETRY = sub { 0 };
+
+    my @captured_args;
+    local *IO::Socket::SSL::start_SSL = sub {
+        my ($class, $fh, @args) = @_;
+        @captured_args = @args;
+        bless $fh, 'IO::Socket::SSL'; # simulate in-place SSL upgrade
+    };
+
+    my $fh = bless( {}, 'IO::Socket::INET' );
+    my $h = bless {
+        fh => $fh,
+        SSL_options => { SSL_create_ctx_callback => $user_cb },
+        verify_SSL  => 0,
+    }, 'HTTP::Tiny::Handle';
+
+    $h->start_ssl('example.com');
+
+    my %args = @captured_args;
+
+    ok( exists $args{SSL_create_ctx_callback},
+        'start_ssl passes SSL_create_ctx_callback to IO::Socket::SSL' );
+    is( ref($args{SSL_create_ctx_callback}), 'CODE',
+        'SSL_create_ctx_callback passed to IO::Socket::SSL is a CODE ref' );
+
+    # Invoke the callback and verify both internal and user callbacks ran
+    $args{SSL_create_ctx_callback}->(my $ctx = {});
+
+    ok( $mode_auto_retry_called,
+        'internal CTX_set_mode/MODE_AUTO_RETRY is called from composed callback' );
+    ok( $user_cb_called,
+        'user SSL_create_ctx_callback is also called from composed callback' );
+}
+
+# Test 3: without a user callback, the internal MODE_AUTO_RETRY callback still fires
+{
+    my $mode_auto_retry_called = 0;
+
+    no warnings 'redefine';
+    local *Net::SSLeay::CTX_set_mode    = sub { $mode_auto_retry_called++ };
+    local *Net::SSLeay::MODE_AUTO_RETRY = sub { 0 };
+
+    my @captured_args;
+    local *IO::Socket::SSL::start_SSL = sub {
+        my ($class, $fh, @args) = @_;
+        @captured_args = @args;
+        bless $fh, 'IO::Socket::SSL';
+    };
+
+    my $fh = bless( {}, 'IO::Socket::INET' );
+    my $h = bless {
+        fh => $fh,
+        SSL_options => {},
+        verify_SSL  => 0,
+    }, 'HTTP::Tiny::Handle';
+
+    $h->start_ssl('example.com');
+
+    my %args = @captured_args;
+    $args{SSL_create_ctx_callback}->(my $ctx = {});
+
+    ok( $mode_auto_retry_called,
+        'internal MODE_AUTO_RETRY still fires when no user callback provided' );
+}
+
+done_testing;