diff --git a/common/src/main/java/dev/cel/common/CelProtoJsonAdapter.java b/common/src/main/java/dev/cel/common/CelProtoJsonAdapter.java
index 74c52f397..1e49b97b9 100644
--- a/common/src/main/java/dev/cel/common/CelProtoJsonAdapter.java
+++ b/common/src/main/java/dev/cel/common/CelProtoJsonAdapter.java
@@ -14,10 +14,14 @@
 
 package dev.cel.common;
 
+import com.google.common.base.CaseFormat;
+import com.google.common.base.Joiner;
 import com.google.common.primitives.UnsignedLong;
 import com.google.errorprone.annotations.Immutable;
 import com.google.protobuf.ByteString;
 import com.google.protobuf.Duration;
+import com.google.protobuf.Empty;
+import com.google.protobuf.FieldMask;
 import com.google.protobuf.ListValue;
 import com.google.protobuf.NullValue;
 import com.google.protobuf.Struct;
@@ -25,7 +29,9 @@
 import com.google.protobuf.Value;
 import com.google.protobuf.util.Durations;
 import com.google.protobuf.util.Timestamps;
+import java.util.ArrayList;
 import java.util.Base64;
+import java.util.List;
 import java.util.Map;
 
 /**
@@ -113,11 +119,36 @@ public static Value adaptValueToJsonValue(Object value) {
       String duration = Durations.toString((Duration) value);
       return json.setStringValue(duration).build();
     }
+    if (value instanceof FieldMask) {
+      String fieldMaskStr = toJsonString((FieldMask) value);
+      return json.setStringValue(fieldMaskStr).build();
+    }
+    if (value instanceof Empty) {
+      // google.protobuf.Empty is just an empty json map {}
+      return json.setStructValue(Struct.getDefaultInstance()).build();
+    }
 
     throw new IllegalArgumentException(
         String.format("Value %s cannot be adapted to a JSON Value.", value));
   }
 
+  /**
+   * Joins the field mask's paths into a single string with commas.
+   * This logic is copied from Protobuf's FieldMaskUtil.java, which we
+   * cannot directly use here due to its dependency to descriptors.
+   */
+  private static String toJsonString(FieldMask fieldMask) {
+    List<String> paths = new ArrayList<>(fieldMask.getPathsCount());
+
+    for (String path : fieldMask.getPathsList()) {
+      if (!path.isEmpty()) {
+        paths.add(CaseFormat.LOWER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, path));
+      }
+    }
+
+    return Joiner.on(",").join(paths);
+  }
+
   /**
    * Adapts an iterable to a JSON list value.
    *
diff --git a/common/src/main/java/dev/cel/common/internal/BUILD.bazel b/common/src/main/java/dev/cel/common/internal/BUILD.bazel
index bca6ec303..9733e0e29 100644
--- a/common/src/main/java/dev/cel/common/internal/BUILD.bazel
+++ b/common/src/main/java/dev/cel/common/internal/BUILD.bazel
@@ -174,6 +174,7 @@ java_library(
         "@maven//:com_google_errorprone_error_prone_annotations",
         "@maven//:com_google_guava_guava",
         "@maven//:com_google_protobuf_protobuf_java",
+        "@maven//:com_google_protobuf_protobuf_java_util",
     ],
 )
 
diff --git a/common/src/main/java/dev/cel/common/internal/ProtoLiteAdapter.java b/common/src/main/java/dev/cel/common/internal/ProtoLiteAdapter.java
index b8aafecff..33d50de12 100644
--- a/common/src/main/java/dev/cel/common/internal/ProtoLiteAdapter.java
+++ b/common/src/main/java/dev/cel/common/internal/ProtoLiteAdapter.java
@@ -96,7 +96,7 @@ public MessageLite adaptValueToWellKnownProto(Object value, WellKnownProto wellK
       case TIMESTAMP:
         return (Timestamp) value;
       default:
-        throw new IllegalArgumentException("Unexpceted wellKnownProto kind: " + wellKnownProto);
+        throw new IllegalArgumentException("Unexpected wellKnownProto kind: " + wellKnownProto);
     }
   }
 
diff --git a/conformance/src/test/java/dev/cel/conformance/BUILD.bazel b/conformance/src/test/java/dev/cel/conformance/BUILD.bazel
index 6025774aa..eae328a13 100644
--- a/conformance/src/test/java/dev/cel/conformance/BUILD.bazel
+++ b/conformance/src/test/java/dev/cel/conformance/BUILD.bazel
@@ -91,10 +91,6 @@ _TESTS_TO_SKIP = [
     "timestamps/timestamp_arithmetic/add_time_to_duration_nanos_negative",
 
     # Skip until fixed.
-    "wrappers/field_mask/to_json",
-    "wrappers/empty/to_json",
-    "wrappers/duration/to_json",
-    "wrappers/timestamp/to_json",
     "fields/qualified_identifier_resolution/map_value_repeat_key_heterogeneous",
     # TODO: Add strings.format and strings.quote.
     "string_ext/quote",