diff --git a/core/src/main/java/org/elasticsearch/plugins/InstallPluginCommand.java b/core/src/main/java/org/elasticsearch/plugins/InstallPluginCommand.java
index 9e17eec2e93..aa224b3c7c3 100644
--- a/core/src/main/java/org/elasticsearch/plugins/InstallPluginCommand.java
+++ b/core/src/main/java/org/elasticsearch/plugins/InstallPluginCommand.java
@@ -237,6 +237,10 @@ class InstallPluginCommand extends SettingCommand {
         }
 
         // fall back to plain old URL
+        if (pluginId.contains("://") == false) {
+            // definitely not a valid url, so assume it is a plugin name
+            throw new UserError(ExitCodes.USAGE, "Unknown plugin " + pluginId);
+        }
         terminal.println("-> Downloading " + URLDecoder.decode(pluginId, "UTF-8"));
         return downloadZip(terminal, pluginId, tmpDir);
     }
diff --git a/qa/evil-tests/src/test/java/org/elasticsearch/plugins/InstallPluginCommandTests.java b/qa/evil-tests/src/test/java/org/elasticsearch/plugins/InstallPluginCommandTests.java
index 5c766018f13..fdf52da2634 100644
--- a/qa/evil-tests/src/test/java/org/elasticsearch/plugins/InstallPluginCommandTests.java
+++ b/qa/evil-tests/src/test/java/org/elasticsearch/plugins/InstallPluginCommandTests.java
@@ -307,6 +307,12 @@ public class InstallPluginCommandTests extends ESTestCase {
         assertTrue(e.getMessage(), e.getMessage().contains("no protocol"));
     }
 
+    public void testUnknownPlugin() throws Exception {
+        Tuple<Path, Environment> env = createEnv(fs, temp);
+        UserError e = expectThrows(UserError.class, () -> installPlugin("foo", env.v1()));
+        assertTrue(e.getMessage(), e.getMessage().contains("Unknown plugin foo"));
+    }
+
     public void testPluginsDirMissing() throws Exception {
         Tuple<Path, Environment> env = createEnv(fs, temp);
         Files.delete(env.v2().pluginsFile());