diff --git a/modules/ingest-grok/src/main/java/org/elasticsearch/ingest/grok/GrokProcessor.java b/modules/ingest-grok/src/main/java/org/elasticsearch/ingest/grok/GrokProcessor.java
index 2c63646ff81..56c04f09709 100644
--- a/modules/ingest-grok/src/main/java/org/elasticsearch/ingest/grok/GrokProcessor.java
+++ b/modules/ingest-grok/src/main/java/org/elasticsearch/ingest/grok/GrokProcessor.java
@@ -19,16 +19,10 @@
 
 package org.elasticsearch.ingest.grok;
 
-import org.elasticsearch.ingest.core.IngestDocument;
 import org.elasticsearch.ingest.core.ConfigurationUtils;
+import org.elasticsearch.ingest.core.IngestDocument;
 import org.elasticsearch.ingest.core.Processor;
 
-import java.io.BufferedReader;
-import java.io.IOException;
-import java.io.InputStream;
-import java.io.InputStreamReader;
-import java.nio.charset.StandardCharsets;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -70,47 +64,17 @@ public final class GrokProcessor implements Processor {
 
     public final static class Factory implements Processor.Factory<GrokProcessor> {
 
-        private final static String[] PATTERN_NAMES = new String[] {
-            "aws", "bacula", "bro", "exim", "firewalls", "grok-patterns", "haproxy",
-            "java", "junos", "linux-syslog", "mcollective-patterns", "mongodb", "nagios",
-            "postgresql", "rails", "redis", "ruby"
-        };
-        private final Map<String, String> builtinPatternBank;
+        private final Map<String, String> builtinPatterns;
 
-        public Factory() throws IOException {
-            // TODO(simonw): we should have a static helper method to load these patterns and make this
-            // factory only accept a String->String map instead. That way we can load
-            // the patterns in the IngestGrokPlugin ctor or even in a static context and this ctor doesn't need to throw any exception.
-            Map<String, String> builtinPatterns = new HashMap<>();
-            for (String pattern : PATTERN_NAMES) {
-                try(InputStream is = getClass().getResourceAsStream("/patterns/" + pattern)) {
-                    loadBankFromStream(builtinPatterns, is);
-                }
-            }
-            this.builtinPatternBank = Collections.unmodifiableMap(builtinPatterns);
-        }
-
-        static void loadBankFromStream(Map<String, String> patternBank, InputStream inputStream) throws IOException {
-            String line;
-            BufferedReader br = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
-            while ((line = br.readLine()) != null) {
-                String trimmedLine = line.replaceAll("^\\s+", "");
-                if (trimmedLine.startsWith("#") || trimmedLine.length() == 0) {
-                    continue;
-                }
-
-                String[] parts = trimmedLine.split("\\s+", 2);
-                if (parts.length == 2) {
-                    patternBank.put(parts[0], parts[1]);
-                }
-            }
+        public Factory(Map<String, String> builtinPatterns) {
+            this.builtinPatterns = builtinPatterns;
         }
 
         public GrokProcessor create(Map<String, Object> config) throws Exception {
             String matchField = ConfigurationUtils.readStringProperty(config, "field");
             String matchPattern = ConfigurationUtils.readStringProperty(config, "pattern");
             Map<String, String> customPatternBank = ConfigurationUtils.readOptionalMap(config, "pattern_definitions");
-            Map<String, String> patternBank = new HashMap<>(builtinPatternBank);
+            Map<String, String> patternBank = new HashMap<>(builtinPatterns);
             if (customPatternBank != null) {
                 patternBank.putAll(customPatternBank);
             }
diff --git a/modules/ingest-grok/src/main/java/org/elasticsearch/ingest/grok/IngestGrokPlugin.java b/modules/ingest-grok/src/main/java/org/elasticsearch/ingest/grok/IngestGrokPlugin.java
index 2b61b5e9073..f6423fe40cf 100644
--- a/modules/ingest-grok/src/main/java/org/elasticsearch/ingest/grok/IngestGrokPlugin.java
+++ b/modules/ingest-grok/src/main/java/org/elasticsearch/ingest/grok/IngestGrokPlugin.java
@@ -22,10 +22,29 @@ package org.elasticsearch.ingest.grok;
 import org.elasticsearch.ingest.IngestModule;
 import org.elasticsearch.plugins.Plugin;
 
+import java.io.BufferedReader;
 import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
 
 public class IngestGrokPlugin extends Plugin {
 
+    private static final String[] PATTERN_NAMES = new String[] {
+        "aws", "bacula", "bro", "exim", "firewalls", "grok-patterns", "haproxy",
+        "java", "junos", "linux-syslog", "mcollective-patterns", "mongodb", "nagios",
+        "postgresql", "rails", "redis", "ruby"
+    };
+
+    private final Map<String, String> builtinPatterns;
+
+    public IngestGrokPlugin() throws IOException {
+        this.builtinPatterns = loadBuiltinPatterns();
+    }
+
     @Override
     public String name() {
         return "ingest-grok";
@@ -37,12 +56,32 @@ public class IngestGrokPlugin extends Plugin {
     }
 
     public void onModule(IngestModule ingestModule) {
-        ingestModule.registerProcessor(GrokProcessor.TYPE, (environment, templateService) -> {
-            try {
-                return new GrokProcessor.Factory();
-            } catch (IOException e) {
-                throw new RuntimeException(e);
+        ingestModule.registerProcessor(GrokProcessor.TYPE, (environment, templateService) -> new GrokProcessor.Factory(builtinPatterns));
+    }
+
+    static Map<String, String> loadBuiltinPatterns() throws IOException {
+        Map<String, String> builtinPatterns = new HashMap<>();
+        for (String pattern : PATTERN_NAMES) {
+            try(InputStream is = IngestGrokPlugin.class.getResourceAsStream("/patterns/" + pattern)) {
+                loadPatterns(builtinPatterns, is);
             }
-        });
+        }
+        return Collections.unmodifiableMap(builtinPatterns);
+    }
+
+    private static void loadPatterns(Map<String, String> patternBank, InputStream inputStream) throws IOException {
+        String line;
+        BufferedReader br = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
+        while ((line = br.readLine()) != null) {
+            String trimmedLine = line.replaceAll("^\\s+", "");
+            if (trimmedLine.startsWith("#") || trimmedLine.length() == 0) {
+                continue;
+            }
+
+            String[] parts = trimmedLine.split("\\s+", 2);
+            if (parts.length == 2) {
+                patternBank.put(parts[0], parts[1]);
+            }
+        }
     }
 }
diff --git a/modules/ingest-grok/src/test/java/org/elasticsearch/ingest/grok/GrokProcessorFactoryTests.java b/modules/ingest-grok/src/test/java/org/elasticsearch/ingest/grok/GrokProcessorFactoryTests.java
index 11c1024eb82..419e48874cd 100644
--- a/modules/ingest-grok/src/test/java/org/elasticsearch/ingest/grok/GrokProcessorFactoryTests.java
+++ b/modules/ingest-grok/src/test/java/org/elasticsearch/ingest/grok/GrokProcessorFactoryTests.java
@@ -19,7 +19,6 @@
 
 package org.elasticsearch.ingest.grok;
 
-import org.elasticsearch.ingest.grok.GrokProcessor;
 import org.elasticsearch.test.ESTestCase;
 
 import java.util.Collections;
@@ -32,7 +31,7 @@ import static org.hamcrest.Matchers.notNullValue;
 public class GrokProcessorFactoryTests extends ESTestCase {
 
     public void testBuild() throws Exception {
-        GrokProcessor.Factory factory = new GrokProcessor.Factory();
+        GrokProcessor.Factory factory = new GrokProcessor.Factory(Collections.emptyMap());
 
         Map<String, Object> config = new HashMap<>();
         config.put("field", "_field");
@@ -43,7 +42,7 @@ public class GrokProcessorFactoryTests extends ESTestCase {
     }
 
     public void testCreateWithCustomPatterns() throws Exception {
-        GrokProcessor.Factory factory = new GrokProcessor.Factory();
+        GrokProcessor.Factory factory = new GrokProcessor.Factory(Collections.emptyMap());
 
         Map<String, Object> config = new HashMap<>();
         config.put("field", "_field");
diff --git a/modules/ingest-grok/src/test/java/org/elasticsearch/ingest/grok/GrokTests.java b/modules/ingest-grok/src/test/java/org/elasticsearch/ingest/grok/GrokTests.java
index 89e44fc7239..21ca17ad713 100644
--- a/modules/ingest-grok/src/test/java/org/elasticsearch/ingest/grok/GrokTests.java
+++ b/modules/ingest-grok/src/test/java/org/elasticsearch/ingest/grok/GrokTests.java
@@ -19,13 +19,10 @@
 
 package org.elasticsearch.ingest.grok;
 
-import org.elasticsearch.ingest.grok.Grok;
-import org.elasticsearch.ingest.grok.GrokProcessor;
 import org.elasticsearch.test.ESTestCase;
 import org.junit.Before;
 
 import java.io.IOException;
-import java.io.InputStream;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
@@ -39,22 +36,9 @@ import static org.hamcrest.Matchers.nullValue;
 public class GrokTests extends ESTestCase {
     private Map<String, String> basePatterns;
 
-    private Map<String, String> newBankFromStreams(InputStream... inputStreams) throws IOException {
-        Map<String, String> patternBank = new HashMap<>();
-
-        for (InputStream is : inputStreams) {
-            GrokProcessor.Factory.loadBankFromStream(patternBank, is);
-        }
-
-        return patternBank;
-    }
-
     @Before
     public void setup() throws IOException {
-        basePatterns = newBankFromStreams(
-                getClass().getResourceAsStream("/patterns/grok-patterns"),
-                getClass().getResourceAsStream("/patterns/linux-syslog")
-        );
+        basePatterns = IngestGrokPlugin.loadBuiltinPatterns();
     }
 
     public void testMatchWithoutCaptures() {