diff --git a/core/src/main/kotlin/ca/allanwang/kau/kotlin/Streams.kt b/core/src/main/kotlin/ca/allanwang/kau/kotlin/Streams.kt
index bfa73fd46..65d15a7bb 100644
--- a/core/src/main/kotlin/ca/allanwang/kau/kotlin/Streams.kt
+++ b/core/src/main/kotlin/ca/allanwang/kau/kotlin/Streams.kt
@@ -24,7 +24,6 @@ package ca.allanwang.kau.kotlin
  * Since we don't have access to the internals of our extended class,
  * We will simply iterate and remove when the filter returns {@code false}
  */
-@Synchronized
 inline fun <T, C : MutableIterable<T>> C.kauRemoveIf(filter: (item: T) -> Boolean): C {
     val iter = iterator()
     while (iter.hasNext())
diff --git a/core/src/main/kotlin/ca/allanwang/kau/permissions/PermissionManager.kt b/core/src/main/kotlin/ca/allanwang/kau/permissions/PermissionManager.kt
index 57a6f42b9..96adfa332 100644
--- a/core/src/main/kotlin/ca/allanwang/kau/permissions/PermissionManager.kt
+++ b/core/src/main/kotlin/ca/allanwang/kau/permissions/PermissionManager.kt
@@ -19,6 +19,7 @@ import android.app.Activity
 import android.content.Context
 import android.content.pm.PackageManager
 import androidx.core.app.ActivityCompat
+import ca.allanwang.kau.kotlin.kauRemoveIf
 import ca.allanwang.kau.kotlin.lazyContext
 import ca.allanwang.kau.logging.KL
 import ca.allanwang.kau.utils.KauException
@@ -30,26 +31,32 @@ import java.lang.ref.WeakReference
 /**
  * Created by Allan Wang on 2017-07-03.
  *
- * Permission manager that is decoupled from activities
- * Keeps track of pending requests, and warns about invalid requests
+ * Permission manager that is decoupled from activities.
+ * Keeps track of pending requests, and warns about invalid requests.
  */
 internal object PermissionManager {
 
-    private var requestInProgress = false
-    private val pendingResults: MutableList<WeakReference<PermissionResult>> by lazy { mutableListOf<WeakReference<PermissionResult>>() }
+    private val pendingResults = mutableListOf<WeakReference<PermissionResult>>()
 
     /**
      * Retrieve permissions requested in our manifest
      */
-    private val manifestPermission = lazyContext<Array<String>> {
+    private val manifestPermission = lazyContext<Set<String>> {
         try {
-            it.packageManager.getPackageInfo(it.packageName, PackageManager.GET_PERMISSIONS)?.requestedPermissions
-                ?: emptyArray()
+            it.packageManager.getPackageInfo(
+                it.packageName,
+                PackageManager.GET_PERMISSIONS
+            )?.requestedPermissions?.toSet()
+                ?: emptySet()
         } catch (e: Exception) {
-            emptyArray()
+            emptySet()
         }
     }
 
+    /**
+     * Registers a new permission request.
+     * It is expected that the callback will be called eventually, unless the parent activity is destroyed.
+     */
     operator fun invoke(
         context: Context,
         permissions: Array<out String>,
@@ -60,13 +67,16 @@ internal object PermissionManager {
         val missingPermissions = permissions.filter { !context.hasPermission(it) }
         if (missingPermissions.isEmpty()) return callback(true, null)
         pendingResults.add(WeakReference(PermissionResult(permissions, callback = callback)))
-        if (!requestInProgress) {
-            requestInProgress = true
+        if (pendingResults.size == 1) {
             requestPermissions(context, missingPermissions.toTypedArray())
-        } else KL.d { "Request is postponed since another one is still in progress; did you remember to override onRequestPermissionsResult?" }
+        } else {
+            KL.d { "Request is postponed since another one is still in progress; did you remember to override onRequestPermissionsResult?" }
+        }
     }
 
-    @Synchronized
+    /**
+     * Checks that the listed permissions can be requested, and submits the request to the provided activity
+     */
     private fun requestPermissions(context: Context, permissions: Array<out String>) {
         permissions.forEach {
             if (!manifestPermission(context).contains(it)) {
@@ -82,29 +92,21 @@ internal object PermissionManager {
     }
 
     /**
-     * Handles permission result by allowing accepted permissions for all pending requests
-     * Also cleans up destroyed or completed pending requests
+     * Handles permission result by allowing accepted permissions for all pending requests.
+     * Also cleans up destroyed or completed pending requests.
      */
     fun onRequestPermissionsResult(context: Context, permissions: Array<out String>, grantResults: IntArray) {
         KL.i { "On permission result: pending ${pendingResults.size}" }
         val count = Math.min(permissions.size, grantResults.size)
-        val iter = pendingResults.iterator()
-        while (iter.hasNext()) {
-            val action = iter.next().get()
-            if ((0 until count).any { action?.onResult(permissions[it], grantResults[it]) != false })
-                iter.remove()
+        pendingResults.kauRemoveIf {
+            val action = it.get()
+            action == null || (0 until count).any { i -> action.onResult(permissions[i], grantResults[i]) }
         }
-        if (pendingResults.isEmpty())
-            requestInProgress = false
-        else {
-            val action = pendingResults.map { it.get() }.firstOrNull { it != null }
-            if (action == null) { //actions have been unlinked from their weak references
-                pendingResults.clear()
-                requestInProgress = false
-                return
-            }
-            requestPermissions(context, action.permissions.toTypedArray())
+        val action = pendingResults.asSequence().map { it.get() }.firstOrNull { it != null }
+        if (action == null) { // actions have been unlinked from their weak references
+            pendingResults.clear()
+            return
         }
-        KL.i { "Post on permission result: pending ${pendingResults.size}" }
+        requestPermissions(context, action.permissions.toTypedArray())
     }
 }
diff --git a/core/src/main/kotlin/ca/allanwang/kau/permissions/PermissionResult.kt b/core/src/main/kotlin/ca/allanwang/kau/permissions/PermissionResult.kt
index 8888c91b7..599f6e85c 100644
--- a/core/src/main/kotlin/ca/allanwang/kau/permissions/PermissionResult.kt
+++ b/core/src/main/kotlin/ca/allanwang/kau/permissions/PermissionResult.kt
@@ -36,7 +36,9 @@ class PermissionResult(permissions: Array<out String>, val callback: (granted: B
             return true
         }
         permissions.remove(permission)
-        if (permissions.isNotEmpty()) return false
+        if (permissions.isNotEmpty()) {
+            return false
+        }
         callback(true, null)
         return true
     }
diff --git a/docs/Changelog.md b/docs/Changelog.md
index 0100e8e6f..a2c38e10c 100644
--- a/docs/Changelog.md
+++ b/docs/Changelog.md
@@ -2,6 +2,7 @@
 
 ## v4.1.0
 * :core: Deprecate NetworkUtils, as the underlying functions are deprecated
+* :core: Permission manager no longer synchronized, as all actions should occur in the main thread
 * :kpref-activity: Getter and setter now have action context, with the option to reload self
 
 ## v4.0.0
diff --git a/sample/src/main/res/xml/kau_changelog.xml b/sample/src/main/res/xml/kau_changelog.xml
index dbaa1ef2e..0b13dd41f 100644
--- a/sample/src/main/res/xml/kau_changelog.xml
+++ b/sample/src/main/res/xml/kau_changelog.xml
@@ -8,9 +8,9 @@
 
     <version title="v4.1.0" />
     <item text=":core: Deprecate NetworkUtils, as the underlying functions are deprecated" />
+    <item text=":core: Permission manager no longer synchronized, as all actions should occur in the main thread" />
     <item text=":kpref-activity: Getter and setter now have action context, with the option to reload self" />
     <item text="" />
-    <item text="" />
 
     <version title="v4.0.0" />
     <item text="Update translations" />