diff --git a/build.zig b/build.zig
index 521aebf..d93b476 100644
--- a/build.zig
+++ b/build.zig
@@ -7,6 +7,8 @@ pub fn build(b: *std.build.Builder) !void {
     // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
     const optimize = b.standardOptimizeOption(.{});
 
+    const use_openssl = b.option(bool, "openssl", "Use system-installed openssl for TLS support in zap") orelse false;
+
     // create a module to be used internally.
     var zap_module = b.createModule(.{
         .source_file = .{ .path = "src/zap.zig" },
@@ -15,7 +17,7 @@ pub fn build(b: *std.build.Builder) !void {
     // register the module so it can be referenced using the package manager.
     try b.modules.put(b.dupe("zap"), zap_module);
 
-    const facilio = try build_facilio("facil.io", b, target, optimize);
+    const facilio = try build_facilio("facil.io", b, target, optimize, use_openssl);
 
     const all_step = b.step("all", "build all examples");
 
diff --git a/facil.io/build.zig b/facil.io/build.zig
index b30ab46..e072242 100644
--- a/facil.io/build.zig
+++ b/facil.io/build.zig
@@ -5,6 +5,7 @@ pub fn build_facilio(
     b: *std.build.Builder,
     target: std.zig.CrossTarget,
     optimize: std.builtin.OptimizeMode,
+    use_openssl: bool,
 ) !*std.build.CompileStep {
     const lib = b.addStaticLibrary(.{
         .name = "facil.io",
@@ -27,6 +28,8 @@ pub fn build_facilio(
     try flags.append("-DFIO_HTTP_EXACT_LOGGING");
     if (target.getAbi() == .musl)
         try flags.append("-D_LARGEFILE64_SOURCE");
+    if (use_openssl)
+        try flags.append("-DHAVE_OPENSSL -DFIO_TLS_FOUND");
 
     // Include paths
     lib.addIncludePath(.{ .path = subdir ++ "/." });
@@ -35,6 +38,8 @@ pub fn build_facilio(
     lib.addIncludePath(.{ .path = subdir ++ "/lib/facil/cli" });
     lib.addIncludePath(.{ .path = subdir ++ "/lib/facil/http" });
     lib.addIncludePath(.{ .path = subdir ++ "/lib/facil/http/parsers" });
+    if (use_openssl)
+        lib.addIncludePath(.{ .path = subdir ++ "/lib/facil/tls" });
 
     // C source files
     lib.addCSourceFiles(&.{
@@ -56,8 +61,22 @@ pub fn build_facilio(
         subdir ++ "/lib/facil/cli/fio_cli.c",
     }, flags.items);
 
+    if (use_openssl) {
+        lib.addCSourceFiles(&.{
+            subdir ++ "/lib/facil/tls/fio_tls_openssl.c",
+            subdir ++ "/lib/facil/tls/fio_tls_missing.c",
+        }, flags.items);
+    }
+
     // link against libc
     lib.linkLibC();
+
+    // link in libopenssl and libcrypto on demand
+    if (use_openssl) {
+        lib.linkSystemLibrary("ssl");
+        lib.linkSystemLibrary("crypto");
+    }
+
     b.installArtifact(lib);
 
     return lib;