diff --git a/core/src/main/java/org/projectnessie/cel/common/types/pb/FieldDescription.java b/core/src/main/java/org/projectnessie/cel/common/types/pb/FieldDescription.java
index 06bf0ab4..fbfd2a3b 100644
--- a/core/src/main/java/org/projectnessie/cel/common/types/pb/FieldDescription.java
+++ b/core/src/main/java/org/projectnessie/cel/common/types/pb/FieldDescription.java
@@ -271,6 +271,9 @@ public Object getFrom(Db db, Object target) {
     if (fieldVal instanceof Message) {
       return maybeUnwrapDynamic(db, (Message) fieldVal);
     }
+    if (fd.isMapField() && fieldVal instanceof Map) {
+      return fieldVal;
+    }
     throw new UnsupportedOperationException("IMPLEMENT ME");
     // TODO implement this
     //    if (field)
@@ -468,18 +471,22 @@ public static Object getValueFromField(FieldDescriptor desc, Message message) {
       if (v instanceof List) {
         List<?> lst = (List<?>) v;
         Map<Object, Object> map = new HashMap<>(lst.size() * 4 / 3 + 1);
+        FieldDescriptor keyDesc = desc.getMessageType().findFieldByNumber(1);
+        FieldDescriptor valueDesc = desc.getMessageType().findFieldByNumber(2);
         for (Object e : lst) {
           Object key;
           Object value;
           if (e instanceof MapEntry) {
-            key = ((MapEntry<?, ?>) e).getKey();
-            value = ((MapEntry<?, ?>) e).getValue();
+            key = normalizeUnsignedValue(keyDesc, ((MapEntry<?, ?>) e).getKey());
+            value = normalizeUnsignedValue(valueDesc, ((MapEntry<?, ?>) e).getValue());
           } else if (e instanceof DynamicMessage) {
             DynamicMessage dynMsg = (DynamicMessage) e;
             List<FieldDescriptor> fields = dynMsg.getDescriptorForType().getFields();
             if (fields.size() == 2) {
-              key = dynMsg.getField(fields.get(0));
-              value = dynMsg.getField(fields.get(1));
+              FieldDescriptor dynKeyDesc = fields.get(0);
+              FieldDescriptor dynValueDesc = fields.get(1);
+              key = normalizeUnsignedValue(dynKeyDesc, dynMsg.getField(dynKeyDesc));
+              value = normalizeUnsignedValue(dynValueDesc, dynMsg.getField(dynValueDesc));
             } else {
               throw new IllegalArgumentException(
                   String.format(
@@ -514,6 +521,18 @@ public static Object getValueFromField(FieldDescriptor desc, Message message) {
     return v;
   }
 
+  private static Object normalizeUnsignedValue(FieldDescriptor desc, Object value) {
+    FieldDescriptor.Type type = desc.getType();
+    if (value instanceof Number
+        && (type == FieldDescriptor.Type.UINT32
+            || type == FieldDescriptor.Type.UINT64
+            || type == FieldDescriptor.Type.FIXED32
+            || type == FieldDescriptor.Type.FIXED64)) {
+      return ULong.valueOf(((Number) value).longValue());
+    }
+    return value;
+  }
+
   private static boolean isWellKnownType(FieldDescriptor desc) {
     if (desc.getJavaType() != JavaType.MESSAGE) {
       return false;
diff --git a/core/src/test/java/org/projectnessie/cel/common/types/pb/FieldDescriptionTest.java b/core/src/test/java/org/projectnessie/cel/common/types/pb/FieldDescriptionTest.java
index 329f2cbb..4f16f048 100644
--- a/core/src/test/java/org/projectnessie/cel/common/types/pb/FieldDescriptionTest.java
+++ b/core/src/test/java/org/projectnessie/cel/common/types/pb/FieldDescriptionTest.java
@@ -25,6 +25,7 @@
 import com.google.api.expr.v1alpha1.Type;
 import com.google.protobuf.BoolValue;
 import com.google.protobuf.Duration;
+import com.google.protobuf.DynamicMessage;
 import com.google.protobuf.Int32Value;
 import com.google.protobuf.Message;
 import com.google.protobuf.NullValue;
@@ -33,6 +34,7 @@
 import com.google.protobuf.Value;
 import java.time.Instant;
 import java.util.Arrays;
+import java.util.Collections;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
@@ -145,6 +147,37 @@ void getFrom(GetFromTestCase tc) {
     assertThat(got).isEqualTo(tc.want);
   }
 
+  @Test
+  void getFromUnsignedMapEntries() {
+    Db pbdb = newDb();
+    TestAllTypes msg =
+        TestAllTypes.newBuilder()
+            .putMapStringUint64("large", -1L)
+            .putMapUint64String(-1L, "large")
+            .putMapUint64Uint64(-1L, Long.MIN_VALUE)
+            .build();
+    String msgName = msg.getDescriptorForType().getFullName();
+    pbdb.registerMessage(msg);
+    PbTypeDescription td = pbdb.describeType(msgName);
+    assertThat(td).isNotNull();
+
+    assertThat(td.fieldByName("map_string_uint64").getFrom(pbdb, msg))
+        .isEqualTo(Collections.singletonMap("large", ULong.valueOf(-1L)));
+    assertThat(td.fieldByName("map_uint64_string").getFrom(pbdb, msg))
+        .isEqualTo(Collections.singletonMap(ULong.valueOf(-1L), "large"));
+    assertThat(td.fieldByName("map_uint64_uint64").getFrom(pbdb, msg))
+        .isEqualTo(Collections.singletonMap(ULong.valueOf(-1L), ULong.valueOf(Long.MIN_VALUE)));
+
+    DynamicMessage dynMsg =
+        DynamicMessage.newBuilder(msg.getDescriptorForType()).mergeFrom(msg).build();
+    assertThat(td.fieldByName("map_string_uint64").getFrom(pbdb, dynMsg))
+        .isEqualTo(Collections.singletonMap("large", ULong.valueOf(-1L)));
+    assertThat(td.fieldByName("map_uint64_string").getFrom(pbdb, dynMsg))
+        .isEqualTo(Collections.singletonMap(ULong.valueOf(-1L), "large"));
+    assertThat(td.fieldByName("map_uint64_uint64").getFrom(pbdb, dynMsg))
+        .isEqualTo(Collections.singletonMap(ULong.valueOf(-1L), ULong.valueOf(Long.MIN_VALUE)));
+  }
+
   static class TestCase {
     Message msg;
     String field;