diff --git a/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteActivity.kt b/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteActivity.kt
index 5f39f37..26a21f9 100644
--- a/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteActivity.kt
+++ b/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteActivity.kt
@@ -28,7 +28,7 @@ import com.afollestad.nocknock.data.model.ValidationMode
 import com.afollestad.nocknock.ui.DarkModeSwitchActivity
 import com.afollestad.nocknock.ui.viewsite.KEY_SITE
 import com.afollestad.nocknock.utilities.ext.onTextChanged
-import com.afollestad.nocknock.utilities.ext.toUri
+import com.afollestad.nocknock.utilities.ext.setTextAndMaintainSelection
 import com.afollestad.nocknock.utilities.livedata.distinct
 import com.afollestad.nocknock.viewcomponents.ext.dimenFloat
 import com.afollestad.nocknock.viewcomponents.ext.onScroll
@@ -141,6 +141,13 @@ class AddSiteActivity : DarkModeSwitchActivity() {
         minutesData = viewModel.retryPolicyMinutes
     )
 
+    // SSL certificate
+    sslCertificateInput.onTextChanged { viewModel.certificateUri.value = it }
+    viewModel.certificateUri.distinct()
+        .observe(this, Observer { sslCertificateInput.setTextAndMaintainSelection(it) })
+    viewModel.onCertificateError()
+        .toViewError(this, sslCertificateInput)
+
     // Headers
     headersLayout.attach(viewModel.headers)
   }
@@ -179,9 +186,6 @@ class AddSiteActivity : DarkModeSwitchActivity() {
     }
 
     // SSL certificate
-    sslCertificateInput.onTextChanged { viewModel.certificateUri.value = it.toUri() }
-    viewModel.certificateUri.distinct()
-        .observe(this, Observer { sslCertificateInput.setText(it.toString()) })
     sslCertificateBrowse.setOnClickListener {
       val intent = Intent(ACTION_OPEN_DOCUMENT).apply {
         addCategory(CATEGORY_OPENABLE)
@@ -193,12 +197,11 @@ class AddSiteActivity : DarkModeSwitchActivity() {
 
   override fun onResume() {
     super.onResume()
-    appToolbar.elevation =
-        if (scrollView.scrollY > appToolbar.measuredHeight / 2) {
-          appToolbar.dimenFloat(R.dimen.default_elevation)
-        } else {
-          0f
-        }
+    appToolbar.elevation = if (scrollView.scrollY > appToolbar.measuredHeight / 2) {
+      appToolbar.dimenFloat(R.dimen.default_elevation)
+    } else {
+      0f
+    }
   }
 
   override fun onActivityResult(
diff --git a/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteViewModel.kt b/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteViewModel.kt
index 3bb7113..87da65c 100644
--- a/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteViewModel.kt
+++ b/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteViewModel.kt
@@ -15,7 +15,6 @@
  */
 package com.afollestad.nocknock.ui.addsite
 
-import android.net.Uri
 import androidx.annotation.CheckResult
 import androidx.annotation.VisibleForTesting
 import androidx.annotation.VisibleForTesting.PRIVATE
@@ -40,6 +39,7 @@ import com.afollestad.nocknock.data.putSite
 import com.afollestad.nocknock.engine.validation.ValidationExecutor
 import com.afollestad.nocknock.ui.ScopedViewModel
 import com.afollestad.nocknock.utilities.ext.MINUTE
+import com.afollestad.nocknock.utilities.ext.toUri
 import com.afollestad.nocknock.utilities.livedata.map
 import com.afollestad.nocknock.viewcomponents.ext.isNullOrLessThan
 import kotlinx.coroutines.CoroutineDispatcher
@@ -69,7 +69,7 @@ class AddSiteViewModel(
   val retryPolicyTimes = MutableLiveData<Int>()
   val retryPolicyMinutes = MutableLiveData<Int>()
   val headers = MutableLiveData<List<Header>>()
-  val certificateUri = MutableLiveData<Uri>()
+  val certificateUri = MutableLiveData<String>()
 
   @OnLifecycleEvent(ON_START)
   fun setDefaults() {
@@ -91,6 +91,7 @@ class AddSiteViewModel(
   private val validationSearchTermError = MutableLiveData<Int?>()
   private val validationScriptError = MutableLiveData<Int?>()
   private val checkIntervalValueError = MutableLiveData<Int?>()
+  private val certificateError = MutableLiveData<Int?>()
 
   // Expose private properties or calculated properties
   @CheckResult fun onIsLoading(): LiveData<Boolean> = isLoading
@@ -130,6 +131,8 @@ class AddSiteViewModel(
 
   @CheckResult fun onCheckIntervalError(): LiveData<Int?> = checkIntervalValueError
 
+  @CheckResult fun onCertificateError(): LiveData<Int?> = certificateError
+
   // Actions
   fun commit(done: () -> Unit) {
     scope.launch {
@@ -228,6 +231,25 @@ class AddSiteViewModel(
       validationScriptError.value = null
     }
 
+    // Validate SSL certificate
+    val certString = certificateUri.value
+    if (certString != null) {
+      val rawCertUri = certString.toUri()
+      val certUri = if (rawCertUri.scheme == null) {
+        rawCertUri.buildUpon()
+            .scheme("file")
+            .build()
+      } else {
+        rawCertUri
+      }
+      if (certUri.scheme != "content" && certUri.scheme != "file") {
+        errorCount++
+        certificateError.value = R.string.please_enter_validCertUri
+      } else {
+        certificateError.value = null
+      }
+    }
+
     if (errorCount > 0) {
       return null
     }
diff --git a/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteActivity.kt b/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteActivity.kt
index 3f83ea0..358dfd1 100644
--- a/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteActivity.kt
+++ b/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteActivity.kt
@@ -28,7 +28,7 @@ import com.afollestad.nocknock.data.model.Site
 import com.afollestad.nocknock.data.model.ValidationMode
 import com.afollestad.nocknock.ui.DarkModeSwitchActivity
 import com.afollestad.nocknock.utilities.ext.onTextChanged
-import com.afollestad.nocknock.utilities.ext.toUri
+import com.afollestad.nocknock.utilities.ext.setTextAndMaintainSelection
 import com.afollestad.nocknock.utilities.livedata.distinct
 import com.afollestad.nocknock.utilities.providers.IntentProvider
 import com.afollestad.nocknock.viewcomponents.ext.dimenFloat
@@ -158,6 +158,13 @@ class ViewSiteActivity : DarkModeSwitchActivity() {
         minutesData = viewModel.retryPolicyMinutes
     )
 
+    // SSL certificate
+    sslCertificateInput.onTextChanged { viewModel.certificateUri.value = it }
+    viewModel.certificateUri.distinct()
+        .observe(this, Observer { sslCertificateInput.setTextAndMaintainSelection(it) })
+    viewModel.onCertificateError()
+        .toViewError(this, sslCertificateInput)
+
     // Headers
     headersLayout.attach(viewModel.headers)
 
@@ -214,7 +221,7 @@ class ViewSiteActivity : DarkModeSwitchActivity() {
               .isVisible = it
         })
 
-    // Done button
+    // Done item text
     viewModel.onDoneButtonText()
         .observe(this, Observer {
           toolbar.menu.findItem(R.id.commit)
@@ -222,9 +229,6 @@ class ViewSiteActivity : DarkModeSwitchActivity() {
         })
 
     // SSL certificate
-    sslCertificateInput.onTextChanged { viewModel.certificateUri.value = it.toUri() }
-    viewModel.certificateUri.distinct()
-        .observe(this, Observer { sslCertificateInput.setText(it.toString()) })
     sslCertificateBrowse.setOnClickListener {
       val intent = Intent(ACTION_OPEN_DOCUMENT).apply {
         addCategory(CATEGORY_OPENABLE)
@@ -236,12 +240,11 @@ class ViewSiteActivity : DarkModeSwitchActivity() {
 
   override fun onResume() {
     super.onResume()
-    appToolbar.elevation =
-        if (scrollView.scrollY > appToolbar.measuredHeight / 2) {
-          appToolbar.dimenFloat(R.dimen.default_elevation)
-        } else {
-          0f
-        }
+    appToolbar.elevation = if (scrollView.scrollY > appToolbar.measuredHeight / 2) {
+      appToolbar.dimenFloat(R.dimen.default_elevation)
+    } else {
+      0f
+    }
   }
 
   override fun onActivityResult(
diff --git a/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModel.kt b/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModel.kt
index 531808d..91c3125 100644
--- a/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModel.kt
+++ b/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModel.kt
@@ -15,7 +15,6 @@
  */
 package com.afollestad.nocknock.ui.viewsite
 
-import android.net.Uri
 import androidx.annotation.CheckResult
 import androidx.annotation.VisibleForTesting
 import androidx.annotation.VisibleForTesting.PRIVATE
@@ -24,9 +23,9 @@ import androidx.lifecycle.LiveData
 import androidx.lifecycle.MutableLiveData
 import com.afollestad.nocknock.R
 import com.afollestad.nocknock.data.AppDatabase
-import com.afollestad.nocknock.data.model.RetryPolicy
 import com.afollestad.nocknock.data.deleteSite
 import com.afollestad.nocknock.data.model.Header
+import com.afollestad.nocknock.data.model.RetryPolicy
 import com.afollestad.nocknock.data.model.Site
 import com.afollestad.nocknock.data.model.Status
 import com.afollestad.nocknock.data.model.Status.WAITING
@@ -41,6 +40,7 @@ import com.afollestad.nocknock.engine.validation.ValidationExecutor
 import com.afollestad.nocknock.notifications.NockNotificationManager
 import com.afollestad.nocknock.ui.ScopedViewModel
 import com.afollestad.nocknock.utilities.ext.formatDate
+import com.afollestad.nocknock.utilities.ext.toUri
 import com.afollestad.nocknock.utilities.livedata.map
 import com.afollestad.nocknock.utilities.livedata.zip
 import com.afollestad.nocknock.utilities.providers.StringProvider
@@ -77,7 +77,7 @@ class ViewSiteViewModel(
   val retryPolicyTimes = MutableLiveData<Int>()
   val retryPolicyMinutes = MutableLiveData<Int>()
   val headers = MutableLiveData<List<Header>>()
-  val certificateUri = MutableLiveData<Uri>()
+  val certificateUri = MutableLiveData<String>()
   internal val disabled = MutableLiveData<Boolean>()
   internal val lastResult = MutableLiveData<ValidationResult?>()
 
@@ -89,6 +89,7 @@ class ViewSiteViewModel(
   private val validationSearchTermError = MutableLiveData<Int?>()
   private val validationScriptError = MutableLiveData<Int?>()
   private val checkIntervalValueError = MutableLiveData<Int?>()
+  private val certificateError = MutableLiveData<Int?>()
 
   // Expose private properties or calculated properties
   @CheckResult fun onIsLoading(): LiveData<Boolean> = isLoading
@@ -131,6 +132,8 @@ class ViewSiteViewModel(
   @CheckResult fun onDisableChecksVisibility(): LiveData<Boolean> =
     disabled.map { !it }
 
+  @CheckResult fun onCertificateError(): LiveData<Int?> = certificateError
+
   @CheckResult fun onDoneButtonText(): LiveData<Int> =
     disabled.map {
       if (it) R.string.renable_and_save_changes
@@ -307,6 +310,25 @@ class ViewSiteViewModel(
       validationScriptError.value = null
     }
 
+    // Validate SSL certificate
+    val certString = certificateUri.value
+    if (certString != null) {
+      val rawCertUri = certString.toUri()
+      val certUri = if (rawCertUri.scheme == null) {
+        rawCertUri.buildUpon()
+            .scheme("file")
+            .build()
+      } else {
+        rawCertUri
+      }
+      if (certUri.scheme != "content" && certUri.scheme != "file") {
+        errorCount++
+        certificateError.value = R.string.please_enter_validCertUri
+      } else {
+        certificateError.value = null
+      }
+    }
+
     if (errorCount > 0) {
       return null
     }
diff --git a/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModelExt.kt b/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModelExt.kt
index 20623ca..3864984 100644
--- a/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModelExt.kt
+++ b/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModelExt.kt
@@ -24,7 +24,6 @@ import com.afollestad.nocknock.utilities.ext.DAY
 import com.afollestad.nocknock.utilities.ext.HOUR
 import com.afollestad.nocknock.utilities.ext.MINUTE
 import com.afollestad.nocknock.utilities.ext.WEEK
-import com.afollestad.nocknock.utilities.ext.toUri
 import kotlin.math.ceil
 
 fun ViewSiteViewModel.setModel(site: Site) {
@@ -56,9 +55,7 @@ fun ViewSiteViewModel.setModel(site: Site) {
   setCheckInterval(settings.validationIntervalMs)
   setRetryPolicy(site.retryPolicy)
   headers.value = site.headers
-  if (settings.certificate != null) {
-    certificateUri.value = settings.certificate!!.toUri()
-  }
+  certificateUri.value = settings.certificate
 
   this.disabled.value = settings.disabled
   this.lastResult.value = site.lastResult
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 6f6e363..2b09271 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -33,6 +33,7 @@
   <string name="please_enter_search_term">Please input a search term.</string>
   <string name="please_enter_javaScript">Please input a validation script.</string>
   <string name="please_enter_networkTimeout">Please enter a network timeout greater than 0.</string>
+  <string name="please_enter_validCertUri">Certificate should be a valid file or content URI.</string>
 
   <string name="options">Options</string>
   <string name="remove_site">Remove Site</string>
diff --git a/common/src/main/java/com/afollestad/nocknock/utilities/ext/ViewExt.kt b/common/src/main/java/com/afollestad/nocknock/utilities/ext/ViewExt.kt
index 86482e3..389de77 100644
--- a/common/src/main/java/com/afollestad/nocknock/utilities/ext/ViewExt.kt
+++ b/common/src/main/java/com/afollestad/nocknock/utilities/ext/ViewExt.kt
@@ -21,7 +21,12 @@ import android.widget.EditText
 import androidx.annotation.IntRange
 import kotlin.math.min
 
-fun EditText.setTextAndMaintainSelection(text: CharSequence) {
+fun EditText.setTextAndMaintainSelection(text: CharSequence?) {
+  if (text == null) {
+    setText("")
+    return
+  }
+
   val formerStart = min(selectionStart, text.length)
   val formerEnd = min(selectionEnd, text.length)
   setText(text)