diff --git a/src/main/kotlin/com/coder/toolbox/views/AuthWizardPage.kt b/src/main/kotlin/com/coder/toolbox/views/AuthWizardPage.kt
index ad0a6de..ca92ed7 100644
--- a/src/main/kotlin/com/coder/toolbox/views/AuthWizardPage.kt
+++ b/src/main/kotlin/com/coder/toolbox/views/AuthWizardPage.kt
@@ -20,7 +20,7 @@ class AuthWizardPage(
 ) : CoderPage(context, context.i18n.ptrl("Authenticate to Coder")) {
     private val shouldAutoLogin = MutableStateFlow(initialAutoLogin)
 
-    private val signInStep = SignInStep(context)
+    private val signInStep = SignInStep(context, this::notify)
     private val tokenStep = TokenStep(context)
     private val connectStep = ConnectStep(context, shouldAutoLogin, this::notify, this::displaySteps, onConnect)
 
diff --git a/src/main/kotlin/com/coder/toolbox/views/SignInStep.kt b/src/main/kotlin/com/coder/toolbox/views/SignInStep.kt
index ffab7ae..488045e 100644
--- a/src/main/kotlin/com/coder/toolbox/views/SignInStep.kt
+++ b/src/main/kotlin/com/coder/toolbox/views/SignInStep.kt
@@ -1,6 +1,7 @@
 package com.coder.toolbox.views
 
 import com.coder.toolbox.CoderToolboxContext
+import com.coder.toolbox.util.toURL
 import com.coder.toolbox.views.state.AuthWizardState
 import com.jetbrains.toolbox.api.localization.LocalizableString
 import com.jetbrains.toolbox.api.ui.components.LabelField
@@ -9,6 +10,7 @@ import com.jetbrains.toolbox.api.ui.components.TextField
 import com.jetbrains.toolbox.api.ui.components.TextType
 import com.jetbrains.toolbox.api.ui.components.ValidationErrorField
 import kotlinx.coroutines.flow.update
+import java.net.MalformedURLException
 
 /**
  * A page with a field for providing the Coder deployment URL.
@@ -16,7 +18,8 @@ import kotlinx.coroutines.flow.update
  * Populates with the provided URL, at which point the user can accept or
  * enter their own.
  */
-class SignInStep(private val context: CoderToolboxContext) : WizardStep {
+class SignInStep(private val context: CoderToolboxContext, private val notify: (String, Throwable) -> Unit) :
+    WizardStep {
     private val urlField = TextField(context.i18n.ptrl("Deployment URL"), "", TextType.General)
     private val descriptionField = LabelField(context.i18n.pnotr(""))
     private val errorField = ValidationErrorField(context.i18n.pnotr(""))
@@ -53,12 +56,28 @@ class SignInStep(private val context: CoderToolboxContext) : WizardStep {
         } else {
             url
         }
-
+        try {
+            validateRawUrl(url)
+        } catch (e: MalformedURLException) {
+            notify("URL is invalid", e)
+            return false
+        }
         context.secrets.lastDeploymentURL = url
         AuthWizardState.goToNextStep()
         return true
     }
 
+    /**
+     * Throws [MalformedURLException] if the given string violates RFC-2396
+     */
+    private fun validateRawUrl(url: String) {
+        try {
+            url.toURL()
+        } catch (e: Exception) {
+            throw MalformedURLException(e.message)
+        }
+    }
+
     override fun onBack() {
         // it's the first step. Can't go anywhere back from here
     }