diff --git a/jvm-runtime/ftl-runtime/common/deployment/src/main/java/xyz/block/ftl/deployment/ModuleBuilder.java b/jvm-runtime/ftl-runtime/common/deployment/src/main/java/xyz/block/ftl/deployment/ModuleBuilder.java
index 98f3c4d93..914c47db2 100644
--- a/jvm-runtime/ftl-runtime/common/deployment/src/main/java/xyz/block/ftl/deployment/ModuleBuilder.java
+++ b/jvm-runtime/ftl-runtime/common/deployment/src/main/java/xyz/block/ftl/deployment/ModuleBuilder.java
@@ -17,7 +17,6 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
-import java.util.function.BiFunction;
 import java.util.function.Consumer;
 import java.util.regex.Pattern;
 
@@ -36,7 +35,6 @@
 
 import com.fasterxml.jackson.annotation.JsonAlias;
 import com.fasterxml.jackson.databind.JsonNode;
-import com.fasterxml.jackson.databind.ObjectMapper;
 
 import io.quarkus.arc.processor.DotNames;
 import xyz.block.ftl.Config;
@@ -73,7 +71,6 @@
 import xyz.block.ftl.schema.v1.TypeAlias;
 import xyz.block.ftl.schema.v1.Unit;
 import xyz.block.ftl.schema.v1.Verb;
-import xyz.block.ftl.v1.CallRequest;
 
 public class ModuleBuilder {
 
@@ -190,7 +187,7 @@ public void registerVerbMethod(MethodInfo method, String className,
             boolean exported, BodyType bodyType, Consumer<Verb.Builder> metadataCallback) {
         try {
             List<Class<?>> parameterTypes = new ArrayList<>();
-            List<BiFunction<ObjectMapper, CallRequest, Object>> paramMappers = new ArrayList<>();
+            List<VerbRegistry.ParameterSupplier> paramMappers = new ArrayList<>();
             org.jboss.jandex.Type bodyParamType = null;
             Nullability bodyParamNullability = Nullability.MISSING;
 
@@ -199,7 +196,9 @@ public void registerVerbMethod(MethodInfo method, String className,
             MetadataCalls.Builder callsMetadata = MetadataCalls.newBuilder();
             MetadataConfig.Builder configMetadata = MetadataConfig.newBuilder();
             MetadataSecrets.Builder secretMetadata = MetadataSecrets.newBuilder();
+            var pos = -1;
             for (var param : method.parameters()) {
+                pos++;
                 if (param.hasAnnotation(Secret.class)) {
                     Class<?> paramType = ModuleBuilder.loadClass(param.type());
                     parameterTypes.add(paramType);
@@ -248,7 +247,7 @@ public void registerVerbMethod(MethodInfo method, String className,
                     Class<?> paramType = ModuleBuilder.loadClass(param.type());
                     parameterTypes.add(paramType);
                     //TODO: map and list types
-                    paramMappers.add(new VerbRegistry.BodySupplier(paramType));
+                    paramMappers.add(new VerbRegistry.BodySupplier(pos));
                 } else {
                     throw new RuntimeException("Unknown parameter type " + param.type() + " on FTL method: "
                             + method.declaringClass().name() + "." + method.name());
diff --git a/jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/runtime/FTLRecorder.java b/jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/runtime/FTLRecorder.java
index 3b67e8e65..8dac19302 100644
--- a/jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/runtime/FTLRecorder.java
+++ b/jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/runtime/FTLRecorder.java
@@ -6,7 +6,6 @@
 import java.util.List;
 import java.util.Timer;
 import java.util.TimerTask;
-import java.util.function.BiFunction;
 
 import org.jboss.resteasy.reactive.server.core.ResteasyReactiveRequestContext;
 import org.jboss.resteasy.reactive.server.core.parameters.ParameterExtractor;
@@ -27,7 +26,7 @@ public class FTLRecorder {
     public static final String X_FTL_VERB = "X-ftl-verb";
 
     public void registerVerb(String module, String verbName, String methodName, List<Class<?>> parameterTypes,
-            Class<?> verbHandlerClass, List<BiFunction<ObjectMapper, CallRequest, Object>> paramMappers,
+            Class<?> verbHandlerClass, List<VerbRegistry.ParameterSupplier> paramMappers,
             boolean allowNullReturn) {
         //TODO: this sucks
         try {
@@ -67,11 +66,11 @@ public void registerEnum(Class<?> ennum, List<Class<?>> variants) {
         }
     }
 
-    public BiFunction<ObjectMapper, CallRequest, Object> topicSupplier(String className, String callingVerb) {
+    public VerbRegistry.ParameterSupplier topicSupplier(String className, String callingVerb) {
         try {
             var cls = Thread.currentThread().getContextClassLoader().loadClass(className.replace("/", "."));
             var topic = cls.getDeclaredConstructor(String.class).newInstance(callingVerb);
-            return new BiFunction<ObjectMapper, CallRequest, Object>() {
+            return new VerbRegistry.ParameterSupplier() {
                 @Override
                 public Object apply(ObjectMapper mapper, CallRequest callRequest) {
                     return topic;
@@ -82,11 +81,11 @@ public Object apply(ObjectMapper mapper, CallRequest callRequest) {
         }
     }
 
-    public BiFunction<ObjectMapper, CallRequest, Object> verbClientSupplier(String className) {
+    public VerbRegistry.ParameterSupplier verbClientSupplier(String className) {
         try {
             var cls = Thread.currentThread().getContextClassLoader().loadClass(className.replace("/", "."));
             var client = cls.getDeclaredConstructor().newInstance();
-            return new BiFunction<ObjectMapper, CallRequest, Object>() {
+            return new VerbRegistry.ParameterSupplier() {
                 @Override
                 public Object apply(ObjectMapper mapper, CallRequest callRequest) {
                     return client;
@@ -97,8 +96,8 @@ public Object apply(ObjectMapper mapper, CallRequest callRequest) {
         }
     }
 
-    public BiFunction<ObjectMapper, CallRequest, Object> leaseClientSupplier() {
-        return new BiFunction<ObjectMapper, CallRequest, Object>() {
+    public VerbRegistry.ParameterSupplier leaseClientSupplier() {
+        return new VerbRegistry.ParameterSupplier() {
 
             @Override
             public Object apply(ObjectMapper mapper, CallRequest callRequest) {
diff --git a/jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/runtime/VerbRegistry.java b/jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/runtime/VerbRegistry.java
index cb9a7e9d6..c02ceb813 100644
--- a/jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/runtime/VerbRegistry.java
+++ b/jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/runtime/VerbRegistry.java
@@ -3,6 +3,7 @@
 import java.io.IOException;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
+import java.lang.reflect.Type;
 import java.nio.charset.StandardCharsets;
 import java.util.List;
 import java.util.Map;
@@ -16,6 +17,7 @@
 import org.jboss.resteasy.reactive.server.core.parameters.ParameterExtractor;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
 import com.google.protobuf.ByteString;
 
 import io.quarkus.arc.Arc;
@@ -37,7 +39,7 @@ public VerbRegistry(ObjectMapper mapper) {
     }
 
     public void register(String module, String name, InstanceHandle<?> verbHandlerClass, Method method,
-            List<BiFunction<ObjectMapper, CallRequest, Object>> paramMappers, boolean allowNullReturn) {
+            List<ParameterSupplier> paramMappers, boolean allowNullReturn) {
         verbs.put(new Key(module, name), new AnnotatedEndpointHandler(verbHandlerClass, method, paramMappers, allowNullReturn));
     }
 
@@ -61,15 +63,18 @@ private record Key(String module, String name) {
     private class AnnotatedEndpointHandler implements VerbInvoker {
         final InstanceHandle<?> verbHandlerClass;
         final Method method;
-        final List<BiFunction<ObjectMapper, CallRequest, Object>> parameterSuppliers;
+        final List<ParameterSupplier> parameterSuppliers;
         final boolean allowNull;
 
         private AnnotatedEndpointHandler(InstanceHandle<?> verbHandlerClass, Method method,
-                List<BiFunction<ObjectMapper, CallRequest, Object>> parameterSuppliers, boolean allowNull) {
+                List<ParameterSupplier> parameterSuppliers, boolean allowNull) {
             this.verbHandlerClass = verbHandlerClass;
             this.method = method;
             this.parameterSuppliers = parameterSuppliers;
             this.allowNull = allowNull;
+            for (ParameterSupplier parameterSupplier : parameterSuppliers) {
+                parameterSupplier.init(method);
+            }
         }
 
         public CallResponse handle(CallRequest in) {
@@ -106,19 +111,36 @@ public CallResponse handle(CallRequest in) {
         }
     }
 
-    public record BodySupplier(Class<?> inputClass) implements BiFunction<ObjectMapper, CallRequest, Object> {
+    public static class BodySupplier implements ParameterSupplier {
+
+        final int parameterIndex;
+        volatile Type inputClass;
+
+        public BodySupplier(int parameterIndex) {
+            this.parameterIndex = parameterIndex;
+        }
+
+        public void init(Method method) {
+            inputClass = method.getGenericParameterTypes()[parameterIndex];
+        }
 
         @Override
         public Object apply(ObjectMapper mapper, CallRequest in) {
             try {
-                return mapper.createParser(in.getBody().newInput()).readValueAs(inputClass);
+                ObjectReader reader = mapper.reader();
+                return reader.forType(reader.getTypeFactory().constructType(inputClass))
+                        .readValue(in.getBody().newInput());
             } catch (IOException e) {
                 throw new RuntimeException(e);
             }
         }
+
+        public int getParameterIndex() {
+            return parameterIndex;
+        }
     }
 
-    public static class SecretSupplier implements BiFunction<ObjectMapper, CallRequest, Object>, ParameterExtractor {
+    public static class SecretSupplier implements ParameterSupplier, ParameterExtractor {
 
         final String name;
         final Class<?> inputClass;
@@ -153,7 +175,7 @@ public Object extractParameter(ResteasyReactiveRequestContext context) {
         }
     }
 
-    public static class ConfigSupplier implements BiFunction<ObjectMapper, CallRequest, Object>, ParameterExtractor {
+    public static class ConfigSupplier implements ParameterSupplier, ParameterExtractor {
 
         final String name;
         final Class<?> inputClass;
@@ -187,4 +209,12 @@ public String getName() {
         }
     }
 
+    public interface ParameterSupplier extends BiFunction<ObjectMapper, CallRequest, Object> {
+
+        // TODO: this is pretty yuck, but it lets us avoid a whole heap of nasty stuff to get the generic type
+        default void init(Method method) {
+
+        }
+
+    }
 }