diff --git a/wire-java-generator/src/main/java/com/squareup/wire/java/JavaGenerator.java b/wire-java-generator/src/main/java/com/squareup/wire/java/JavaGenerator.java
index 5c00bd2bfd..d4bc4eedac 100644
--- a/wire-java-generator/src/main/java/com/squareup/wire/java/JavaGenerator.java
+++ b/wire-java-generator/src/main/java/com/squareup/wire/java/JavaGenerator.java
@@ -58,7 +58,7 @@
 import com.squareup.wire.schema.Service;
 import com.squareup.wire.schema.Type;
 import java.io.IOException;
-import java.math.BigDecimal;
+import java.math.BigInteger;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -1500,14 +1500,10 @@ private CodeBlock fieldInitializer(ProtoType type, Object value) {
       return CodeBlock.of("$L", value != null ? value : false);
 
     } else if (javaType.equals(TypeName.INT.box())) {
-      return CodeBlock.of("$L", value != null
-          ? new BigDecimal(String.valueOf(value)).intValue()
-          : 0);
+      return CodeBlock.of("$L", valueToInt(value));
 
     } else if (javaType.equals(TypeName.LONG.box())) {
-      return CodeBlock.of("$LL", value != null
-          ? Long.toString(new BigDecimal(String.valueOf(value)).longValue())
-          : 0L);
+      return CodeBlock.of("$LL", Long.toString(valueToLong(value)));
 
     } else if (javaType.equals(TypeName.FLOAT.box())) {
       return CodeBlock.of("$Lf", value != null ? String.valueOf(value) : 0f);
@@ -1533,4 +1529,30 @@ private CodeBlock fieldInitializer(ProtoType type, Object value) {
       throw new IllegalStateException(type + " is not an allowed scalar type");
     }
   }
+
+  static int valueToInt(Object value) {
+    if (value == null) return 0;
+
+    String string = String.valueOf(value);
+    if (string.startsWith("0x") || string.startsWith("0X")) {
+      return Integer.valueOf(string.substring("0x".length()), 16); // Hexadecimal.
+    } else if (string.startsWith("0") && !string.equals("0")) {
+      throw new IllegalStateException("Octal literal unsupported: " + value); // Octal.
+    } else {
+      return new BigInteger(string).intValue(); // Decimal.
+    }
+  }
+
+  static long valueToLong(Object value) {
+    if (value == null) return 0L;
+
+    String string = String.valueOf(value);
+    if (string.startsWith("0x") || string.startsWith("0X")) {
+      return Long.valueOf(string.substring("0x".length()), 16); // Hexadecimal.
+    } else if (string.startsWith("0") && !string.equals("0")) {
+      throw new IllegalStateException("Octal literal unsupported: " + value); // Octal.
+    } else {
+      return new BigInteger(string).longValue(); // Decimal.
+    }
+  }
 }
diff --git a/wire-tests/src/test/java/com/squareup/wire/java/JavaGeneratorTest.java b/wire-tests/src/test/java/com/squareup/wire/java/JavaGeneratorTest.java
index 58b7e88466..9a9f402c2a 100644
--- a/wire-tests/src/test/java/com/squareup/wire/java/JavaGeneratorTest.java
+++ b/wire-tests/src/test/java/com/squareup/wire/java/JavaGeneratorTest.java
@@ -24,6 +24,7 @@
 import org.junit.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.fail;
 
 public final class JavaGeneratorTest {
   @Test public void sanitizeJavadocStripsTrailingWhitespace() {
@@ -237,4 +238,36 @@ public final class JavaGeneratorTest {
     assertThat(repoBuilder.generateCode("A", "android")).contains(""
         + "  public abstract static class AbstractBAdapter extends ProtoAdapter<String> {\n");
   }
+
+  /** https://github.com/square/wire/issues/655 */
+  @Test public void defaultValues() throws IOException {
+    RepoBuilder repoBuilder = new RepoBuilder()
+        .add("message.proto", ""
+            + "message Message {\n"
+            + "  optional int32 a = 1 [default = 10 ];\n"
+            + "  optional int32 b = 2 [default = 0x20 ];\n"
+            + "  optional int64 c = 3 [default = 11 ];\n"
+            + "  optional int64 d = 4 [default = 0x21 ];\n"
+            + "}\n");
+    String code = repoBuilder.generateCode("Message");
+    assertThat(code).contains("  public static final Integer DEFAULT_A = 10;");
+    assertThat(code).contains("  public static final Integer DEFAULT_B = 32;");
+    assertThat(code).contains("  public static final Long DEFAULT_C = 11L;");
+    assertThat(code).contains("  public static final Long DEFAULT_D = 33L;");
+  }
+
+  @Test public void defaultValuesMustNotBeOctal() throws IOException {
+    RepoBuilder repoBuilder = new RepoBuilder()
+        .add("message.proto", ""
+            + "message Message {\n"
+            + "  optional int32 a = 1 [default = 020 ];\n"
+            + "  optional int64 b = 2 [default = 021 ];\n"
+            + "}\n");
+    try {
+      repoBuilder.generateCode("Message");
+      fail();
+    } catch (IllegalStateException expected) {
+      assertThat(expected).hasMessage("Octal literal unsupported: 020");
+    }
+  }
 }