diff --git a/src/main/java/com/android/tools/r8/retrace/Retrace.java b/src/main/java/com/android/tools/r8/retrace/Retrace.java
index 0edcea8..6616a66 100644
--- a/src/main/java/com/android/tools/r8/retrace/Retrace.java
+++ b/src/main/java/com/android/tools/r8/retrace/Retrace.java
@@ -35,6 +35,13 @@
 @Keep
 public class Retrace {
 
+  // This is a slight modification of the default regular expression shown for proguard retrace
+  // that allow for retracing classes in the form <class>: lorem ipsum...
+  // Seems like Proguard retrace is expecting the form "Caused by: <class>".
+  public static final String DEFAULT_REGULAR_EXPRESSION =
+      "(?:.*?\\bat\\s+%c\\.%m\\s*\\(%s(?::%l)?\\)\\s*(?:~\\[.*\\])?)"
+          + "|(?:(?:(?:%c|.*)?[:\"]\\s+)?%c(?::.*)?)";
+
   public static final String USAGE_MESSAGE =
       StringUtils.lines(
           "Usage: retrace <proguard-map> <stacktrace-file> [--regex <regexp>, --verbose, --info]",
@@ -45,6 +52,7 @@
     Builder builder = RetraceCommand.builder(diagnosticsHandler);
     boolean hasSetProguardMap = false;
     boolean hasSetStackTrace = false;
+    boolean hasSetRegularExpression = false;
     while (context.head() != null) {
       Boolean help = OptionsParsing.tryParseBoolean(context, "--help");
       if (help != null) {
@@ -63,6 +71,7 @@
       String regex = OptionsParsing.tryParseSingle(context, "--regex", "r");
       if (regex != null && !regex.isEmpty()) {
         builder.setRegularExpression(regex);
+        hasSetRegularExpression = true;
         continue;
       }
       if (!hasSetProguardMap) {
@@ -88,6 +97,9 @@
     if (!hasSetStackTrace) {
       builder.setStackTrace(getStackTraceFromStandardInput());
     }
+    if (!hasSetRegularExpression) {
+      builder.setRegularExpression(DEFAULT_REGULAR_EXPRESSION);
+    }
     return builder;
   }
 
diff --git a/src/test/java/com/android/tools/r8/retrace/RetraceCommandLineTests.java b/src/test/java/com/android/tools/r8/retrace/RetraceCommandLineTests.java
index 102f7f0..406eb5c 100644
--- a/src/test/java/com/android/tools/r8/retrace/RetraceCommandLineTests.java
+++ b/src/test/java/com/android/tools/r8/retrace/RetraceCommandLineTests.java
@@ -4,7 +4,6 @@
 
 package com.android.tools.r8.retrace;
 
-import static com.android.tools.r8.retrace.RetraceTests.DEFAULT_REGULAR_EXPRESSION;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.core.StringContains.containsString;
 import static org.junit.Assert.assertEquals;
@@ -76,8 +75,7 @@
         stackTrace.mapping(),
         StringUtils.joinLines(stackTrace.obfuscatedStackTrace()),
         false,
-        StringUtils.joinLines(stackTrace.retracedStackTrace()) + StringUtils.LINE_SEPARATOR,
-        "--regex=" + DEFAULT_REGULAR_EXPRESSION);
+        StringUtils.joinLines(stackTrace.retracedStackTrace()) + StringUtils.LINE_SEPARATOR);
   }
 
   @Test
@@ -88,7 +86,6 @@
         StringUtils.joinLines(stackTrace.obfuscatedStackTrace()),
         false,
         StringUtils.joinLines(stackTrace.retracedStackTrace()) + StringUtils.LINE_SEPARATOR,
-        "--regex=" + DEFAULT_REGULAR_EXPRESSION,
         "--info");
   }
 
diff --git a/src/test/java/com/android/tools/r8/retrace/RetraceTests.java b/src/test/java/com/android/tools/r8/retrace/RetraceTests.java
index 47dc5c3..9af9e28 100644
--- a/src/test/java/com/android/tools/r8/retrace/RetraceTests.java
+++ b/src/test/java/com/android/tools/r8/retrace/RetraceTests.java
@@ -4,6 +4,7 @@
 
 package com.android.tools.r8.retrace;
 
+import static com.android.tools.r8.retrace.Retrace.DEFAULT_REGULAR_EXPRESSION;
 import static junit.framework.TestCase.assertEquals;
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.MatcherAssert.assertThat;
@@ -45,12 +46,6 @@
 @RunWith(Parameterized.class)
 public class RetraceTests extends TestBase {
 
-  // This is a slight modification of the default regular expression shown for proguard retrace
-  // that allow for retracing classes in the form <class>: lorem ipsum...
-  // Seems like Proguard retrace is expecting the form "Caused by: <class>".
-  public static final String DEFAULT_REGULAR_EXPRESSION =
-      "(?:.*?\\bat\\s+%c\\.%m\\s*\\(%s(?::%l)?\\)\\s*(?:~\\[.*\\])?)|(?:(?:(?:%c|.*)?[:\"]\\s+)?%c(?::.*)?)";
-
   @Parameters(name = "{0}, use regular expression: {1}")
   public static Collection<Object[]> data() {
     return buildParameters(getTestParameters().withNoneRuntime().build(), BooleanUtils.values());