diff --git a/watchid-pam-extension.swift b/watchid-pam-extension.swift
index f10d272..64d5153 100644
--- a/watchid-pam-extension.swift
+++ b/watchid-pam-extension.swift
@@ -2,24 +2,25 @@ import LocalAuthentication
 
 // MARK: (Re)define PAM constants here so we don't need to import .h files.
 
-private let PAM_SUCCESS = 0
-private let PAM_AUTH_ERR = 9
-private let PAM_IGNORE = 25
+private let PAM_SUCCESS = CInt(0)
+private let PAM_AUTH_ERR = CInt(9)
+private let PAM_IGNORE = CInt(25)
+private let PAM_SILENT = CInt(bitPattern: 0x80000000)
 private let DEFAULT_REASON = "perform an action that requires authentication"
 
-public typealias vchar = UnsafeMutablePointer<UnsafeMutablePointer<Int8>>
-public typealias pam_handler_t = UnsafeRawPointer
+public typealias vchar = UnsafePointer<UnsafeMutablePointer<CChar>>
+public typealias pam_handle_t = UnsafeRawPointer?
 
 // MARK: Biometric (touchID) authentication
 
-@_silgen_name("pam_sm_authenticate")
-public func pam_sm_authenticate(pamh: pam_handler_t, flags: Int, argc: Int, argv: vchar) -> Int {
+@_cdecl("pam_sm_authenticate")
+public func pam_sm_authenticate(pamh: pam_handle_t, flags: CInt, argc: CInt, argv: vchar) -> CInt {
     let sudoArguments = ProcessInfo.processInfo.arguments
     if sudoArguments.contains("-A") || sudoArguments.contains("--askpass") {
         return PAM_IGNORE
     }
 
-    let arguments = parseArguments(argc: argc, argv: argv)
+    let arguments = parseArguments(argc: Int(argc), argv: argv)
     var reason = arguments["reason"] ?? DEFAULT_REASON
     reason = reason.isEmpty ? DEFAULT_REASON : reason
 
@@ -36,7 +37,9 @@ public func pam_sm_authenticate(pamh: pam_handler_t, flags: Int, argc: Int, argv
         defer { semaphore.signal() }
 
         if let error = error {
-            fputs("\(error.localizedDescription)\n", stderr)			
+            if flags & PAM_SILENT == 0 {
+                fputs("\(error.localizedDescription)\n", stderr)
+            }
             result = PAM_IGNORE
             return
         }
@@ -50,8 +53,8 @@ public func pam_sm_authenticate(pamh: pam_handler_t, flags: Int, argc: Int, argv
 
 private func parseArguments(argc: Int, argv: vchar) -> [String: String] {
     var parsed = [String: String]()
-    let arguments = (0 ..< argc)
-       .map { String(cString: argv[$0]) }
+    let arguments = UnsafeBufferPointer(start: argv, count: argc)
+       .compactMap { String(cString: $0) }
        .joined(separator: " ")
 
     let regex = try? NSRegularExpression(pattern: "[^\\s\"']+|\"([^\"]*)\"|'([^']*)'",
@@ -83,17 +86,17 @@ private extension LAPolicy {
 
 // MARK: - Ignored (unhandled) PAM events
 
-@_silgen_name("pam_sm_chauthtok")
-public func pam_sm_chauthtok(pamh: pam_handler_t, flags: Int, argc: Int, argv: vchar) -> Int {
+@_cdecl("pam_sm_chauthtok")
+public func pam_sm_chauthtok(pamh: pam_handle_t, flags: CInt, argc: CInt, argv: vchar) -> CInt {
     return PAM_IGNORE
 }
 
-@_silgen_name("pam_sm_setcred")
-public func pam_sm_setcred(pamh: pam_handler_t, flags: Int, argc: Int, argv: vchar) -> Int {
+@_cdecl("pam_sm_setcred")
+public func pam_sm_setcred(pamh: pam_handle_t, flags: CInt, argc: CInt, argv: vchar) -> CInt {
     return PAM_IGNORE
 }
 
-@_silgen_name("pam_sm_acct_mgmt")
-public func pam_sm_acct_mgmt(pamh: pam_handler_t, flags: Int, argc: Int, argv: vchar) -> Int {
+@_cdecl("pam_sm_acct_mgmt")
+public func pam_sm_acct_mgmt(pamh: pam_handle_t, flags: CInt, argc: CInt, argv: vchar) -> CInt {
     return PAM_IGNORE
 }