diff --git a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoCompileActionBuilder.java b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoCompileActionBuilder.java
index 7f4b2daa3ec174..3b27faea755aa9 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoCompileActionBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoCompileActionBuilder.java
@@ -53,7 +53,7 @@
 public class ProtoCompileActionBuilder {
   @VisibleForTesting
   public static final String STRICT_DEPS_FLAG_TEMPLATE =
-      "--direct_dependencies_violation_msg=" + StrictProtoDepsViolationMessage.MESSAGE;
+      "--direct_dependencies_violation_msg=" + ProtoConstants.STRICT_PROTO_DEPS_VIOLATION_MESSAGE;
 
   private static final String MNEMONIC = "GenProto";
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
index 466bbe713aa289..7b1e2c018bb67a 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
@@ -38,6 +38,7 @@
 // configuration fragment in aspect definitions.
 @RequiresOptions(options = {ProtoConfiguration.Options.class})
 public class ProtoConfiguration extends Fragment implements ProtoConfigurationApi {
+
   /** Command line options. */
   public static class Options extends FragmentOptions {
     @Option(
@@ -81,7 +82,7 @@ public static class Options extends FragmentOptions {
 
     @Option(
         name = "proto_compiler",
-        defaultValue = "@com_google_protobuf//:protoc",
+        defaultValue = ProtoConstants.DEFAULT_PROTOC_LABEL,
         converter = CoreOptionConverters.LabelConverter.class,
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.AFFECTS_OUTPUTS, OptionEffectTag.LOADING_AND_ANALYSIS},
@@ -219,7 +220,10 @@ public boolean runExperimentalProtoExtraActions() {
     return options.experimentalProtoExtraActions;
   }
 
-  @StarlarkConfigurationField(name = "proto_compiler", doc = "Label for the proto compiler.")
+  @StarlarkConfigurationField(
+      name = "proto_compiler",
+      doc = "Label for the proto compiler.",
+      defaultLabel = ProtoConstants.DEFAULT_PROTOC_LABEL)
   public Label protoCompiler() {
     return options.protoCompiler;
   }
diff --git a/src/main/java/com/google/devtools/build/lib/rules/proto/StrictProtoDepsViolationMessage.java b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConstants.java
similarity index 51%
rename from src/main/java/com/google/devtools/build/lib/rules/proto/StrictProtoDepsViolationMessage.java
rename to src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConstants.java
index 6d6d03844d1b64..419756cae76a92 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/proto/StrictProtoDepsViolationMessage.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConstants.java
@@ -14,16 +14,22 @@
 
 package com.google.devtools.build.lib.rules.proto;
 
-/**
- * This class is used in ProtoCompileActionBuilder to generate an error message that's displayed
- * when a strict proto deps violation occurs.
- *
- * <p>%1$s is replaced with the label of the proto_library rule that's currently being built.
- *
- * <p>%%s is replaced with the literal "%s", which is passed to the proto-compiler, which replaces
- * it with the .proto file that violates strict proto deps.
- */
-public class StrictProtoDepsViolationMessage {
-  static final String MESSAGE =
+/** Constants used in Proto rules. */
+public final class ProtoConstants {
+  /** Default label for proto compiler. */
+  static final String DEFAULT_PROTOC_LABEL =  "@com_google_protobuf//:protoc";
+
+  /**
+   * This constant is used in ProtoCompileActionBuilder to generate an error message that's
+   * displayed when a strict proto deps violation occurs.
+   *
+   * <p>%1$s is replaced with the label of the proto_library rule that's currently being built.
+   *
+   * <p>%%s is replaced with the literal "%s", which is passed to the proto-compiler, which replaces
+   * it with the .proto file that violates strict proto deps.
+   */
+  static final String STRICT_PROTO_DEPS_VIOLATION_MESSAGE =
       "%%s is imported, but %1$s doesn't directly depend on a proto_library that 'srcs' it.";
+
+  private ProtoConstants() {}
 }