diff --git a/json-path/src/main/java/com/jayway/jsonpath/Configuration.java b/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
index 1a591ea8d..ff54ab6fb 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
@@ -23,6 +23,7 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.EnumSet;
+import java.util.Map;
 import java.util.Set;
 
 import static com.jayway.jsonpath.internal.Utils.notNull;
@@ -55,8 +56,10 @@ private static Defaults getEffectiveDefaults(){
     private final MappingProvider mappingProvider;
     private final Set<Option> options;
     private final Collection<EvaluationListener> evaluationListeners;
+    private final Map<String, Class> functionMap;
 
-    private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider, EnumSet<Option> options, Collection<EvaluationListener> evaluationListeners) {
+    private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider, EnumSet<Option> options,
+                          Collection<EvaluationListener> evaluationListeners, Map<String, Class> functionMap) {
         notNull(jsonProvider, "jsonProvider can not be null");
         notNull(mappingProvider, "mappingProvider can not be null");
         notNull(options, "setOptions can not be null");
@@ -65,6 +68,7 @@ private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider
         this.mappingProvider = mappingProvider;
         this.options = Collections.unmodifiableSet(options);
         this.evaluationListeners = Collections.unmodifiableCollection(evaluationListeners);
+        this.functionMap = functionMap;
     }
 
     /**
@@ -127,6 +131,15 @@ public MappingProvider mappingProvider() {
         return mappingProvider;
     }
 
+    /**
+     * Returns {@link com.jayway.jsonpath.internal.function.PathFunction} defined in functionMap.
+     * @param name
+     * @return null if there are no functionMap defined or the function is not defined.
+     */
+    public Map<String, Class> getFunctionMap() {
+        return functionMap;
+    }
+
     /**
      * Creates a new configuration by adding the new options to the options used in this configuration.
      * @param options options to add
@@ -189,6 +202,8 @@ public static class ConfigurationBuilder {
 
         private JsonProvider jsonProvider;
         private MappingProvider mappingProvider;
+        private Map<String, Class> functionMap;
+
         private EnumSet<Option> options = EnumSet.noneOf(Option.class);
         private Collection<EvaluationListener> evaluationListener = new ArrayList<EvaluationListener>();
 
@@ -202,6 +217,11 @@ public ConfigurationBuilder mappingProvider(MappingProvider provider) {
             return this;
         }
 
+        public ConfigurationBuilder functionMap(Map<String, Class> functionMap) {
+            this.functionMap = functionMap;
+            return this;
+        }
+
         public ConfigurationBuilder options(Option... flags) {
             if(flags.length > 0) {
                 this.options.addAll(asList(flags));
@@ -234,7 +254,7 @@ public Configuration build() {
                     mappingProvider = defaults.mappingProvider();
                 }
             }
-            return new Configuration(jsonProvider, mappingProvider, options, evaluationListener);
+            return new Configuration(jsonProvider, mappingProvider, options, evaluationListener, functionMap);
         }
     }
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
index a35f61bf3..6b0272123 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
@@ -1,5 +1,6 @@
 package com.jayway.jsonpath.internal.function;
 
+import com.jayway.jsonpath.Configuration;
 import com.jayway.jsonpath.InvalidPathException;
 import com.jayway.jsonpath.internal.function.json.Append;
 import com.jayway.jsonpath.internal.function.numeric.Average;
@@ -64,8 +65,17 @@ public class PathFunctionFactory {
      *
      * @throws InvalidPathException
      */
-    public static PathFunction newFunction(String name) throws InvalidPathException {
-        Class functionClazz = FUNCTIONS.get(name);
+    public static PathFunction newFunction(String name, Configuration conf) throws InvalidPathException {
+        Class functionClazz = null;
+        if (conf != null && conf.getFunctionMap() != null) {
+            Map<String, Class> confFunctionMap = conf.getFunctionMap();
+            functionClazz = confFunctionMap.get(name);
+        }
+
+        if (functionClazz == null) {
+            functionClazz = FUNCTIONS.get(name);
+        }
+
         if(functionClazz == null){
             throw new InvalidPathException("Function with name: " + name + " does not exist.");
         } else {
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
index b15638150..b77907cb0 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
@@ -35,7 +35,7 @@ public FunctionPathToken(String pathFragment, List<Parameter> parameters) {
 
     @Override
     public void evaluate(String currentPath, PathRef parent, Object model, EvaluationContextImpl ctx) {
-        PathFunction pathFunction = PathFunctionFactory.newFunction(functionName);
+        PathFunction pathFunction = PathFunctionFactory.newFunction(functionName, ctx.configuration());
         evaluateParameters(currentPath, parent, model, ctx);
         Object result = pathFunction.invoke(currentPath, parent, model, ctx, functionParams);
         ctx.addResult(currentPath + "." + functionName, parent, result);
diff --git a/json-path/src/test/java/com/jayway/jsonpath/internal/function/FunctionDefinitionTest.java b/json-path/src/test/java/com/jayway/jsonpath/internal/function/FunctionDefinitionTest.java
new file mode 100644
index 000000000..cd5a3028e
--- /dev/null
+++ b/json-path/src/test/java/com/jayway/jsonpath/internal/function/FunctionDefinitionTest.java
@@ -0,0 +1,60 @@
+package com.jayway.jsonpath.internal.function;
+
+import com.jayway.jsonpath.Configuration;
+import com.jayway.jsonpath.Configurations;
+import com.jayway.jsonpath.InvalidPathException;
+import com.jayway.jsonpath.internal.EvaluationContext;
+import com.jayway.jsonpath.internal.PathRef;
+import com.jayway.jsonpath.internal.function.numeric.Max;
+import com.jayway.jsonpath.spi.json.GsonJsonProvider;
+import com.jayway.jsonpath.spi.mapper.GsonMappingProvider;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class ToLowerPathFunction implements PathFunction {
+    @Override
+    public Object invoke(String currentPath, PathRef parent, Object model, EvaluationContext ctx, List<Parameter> parameters) {
+        return ((String) model).toLowerCase();
+    }
+}
+
+public class FunctionDefinitionTest extends BaseFunctionTest {
+
+    @Test
+    public void testToLowerFunction() throws IllegalAccessException, InstantiationException {
+        Map<String, Class> funcMap = new HashMap<String, Class>();
+        funcMap.put("toLower", ToLowerPathFunction.class);
+        Configuration conf = Configuration
+                .builder()
+                .mappingProvider(new GsonMappingProvider())
+                .jsonProvider(new GsonJsonProvider())
+                .functionMap(funcMap)
+                .build();
+
+        verifyFunction(conf, "$.upper.toLower()", "{\"upper\":\"UPPERCASE\"}", "uppercase");
+    }
+
+    @Test
+    public void testUndefinedFunction() throws IllegalAccessException, InstantiationException {
+        Map<String, Class> funcMap = new HashMap<String, Class>();
+        funcMap.put("toLower", ToLowerPathFunction.class);
+        Configuration conf = Configuration
+                .builder()
+                .mappingProvider(new GsonMappingProvider())
+                .jsonProvider(new GsonJsonProvider())
+                .functionMap(funcMap)
+                .build();
+        boolean caughtException = false;
+        try {
+            verifyFunction(conf, "$.upper.undefined()", "{\"upper\":\"UPPERCASE\"}", "uppercase");
+        } catch (InvalidPathException exp) {
+            caughtException=true;
+        }
+        assertThat(caughtException);
+    }
+}