diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
index 873d85e..831c408 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
@@ -151,17 +151,22 @@
       repo = absName;
       absName = "//:" + absName.substring(1);
     }
+    String error = RepositoryName.validate(repo);
+    if (error != null) {
+      throw new LabelSyntaxException(
+          "invalid repository name '" + StringUtilities.sanitizeControlChars(repo) + "': " + error);
+    }
     try {
       LabelValidator.PackageAndTarget labelParts = LabelValidator.parseAbsoluteLabel(absName);
-      PackageIdentifier pkgIdWithoutRepo =
-          validatePackageName(labelParts.getPackageName(), labelParts.getTargetName());
-      PathFragment packageFragment = pkgIdWithoutRepo.getPackageFragment();
+      PackageIdentifier pkgId =
+          validatePackageName(
+              labelParts.getPackageName(), labelParts.getTargetName(), repo, repositoryMapping);
+      PathFragment packageFragment = pkgId.getPackageFragment();
       if (repo.isEmpty() && ABSOLUTE_PACKAGE_NAMES.contains(packageFragment)) {
-        repo = "@";
+        pkgId =
+            PackageIdentifier.create(getGlobalRepoName("@", repositoryMapping), packageFragment);
       }
-      RepositoryName globalRepoName = getGlobalRepoName(repo, repositoryMapping);
-      return create(
-          PackageIdentifier.create(globalRepoName, packageFragment), labelParts.getTargetName());
+      return create(pkgId, labelParts.getTargetName());
     } catch (BadLabelException e) {
       throw new LabelSyntaxException(e.getMessage());
     }
@@ -288,15 +293,25 @@
     return name;
   }
 
+  private static PackageIdentifier validatePackageName(String packageIdentifier, String name)
+      throws LabelSyntaxException {
+    return validatePackageName(
+        packageIdentifier, name, /* repo= */ null, /* repositoryMapping= */ null);
+  }
+
   /**
    * Validates the given package name and returns a canonical {@link PackageIdentifier} instance if
    * it is valid. Otherwise it throws a SyntaxException.
    */
-  private static PackageIdentifier validatePackageName(String packageIdentifier, String name)
+  private static PackageIdentifier validatePackageName(
+      String packageIdentifier,
+      String name,
+      String repo,
+      ImmutableMap<RepositoryName, RepositoryName> repositoryMapping)
       throws LabelSyntaxException {
     String error = null;
     try {
-      return PackageIdentifier.parse(packageIdentifier);
+      return PackageIdentifier.parse(packageIdentifier, repo, repositoryMapping);
     } catch (LabelSyntaxException e) {
       error = e.getMessage();
       error = "invalid package name '" + packageIdentifier + "': " + error;
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/LabelValidator.java b/src/main/java/com/google/devtools/build/lib/cmdline/LabelValidator.java
index 633946c..e63b096 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/LabelValidator.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/LabelValidator.java
@@ -45,7 +45,6 @@
   // Package names allow all 7-bit ASCII characters except
   // 0-31 (control characters)
   // 58 ':' (colon) - target name separator
-  // 64 '@' (at-sign) - workspace name prefix
   // 92 '\' (backslash) - directory separator (on Windows); may be allowed in the future
   // 127 (delete)
   /** Matches characters allowed in package name. */
@@ -53,7 +52,7 @@
       CharMatcher.inRange('0', '9')
           .or(CharMatcher.inRange('a', 'z'))
           .or(CharMatcher.inRange('A', 'Z'))
-          .or(CharMatcher.anyOf(" !\"#$%&'()*+,-./;<=>?[]^_`{|}~"))
+          .or(CharMatcher.anyOf(" !\"#$%&'()*+,-./;<=>?@[]^_`{|}~"))
           .precomputed();
 
   /**
@@ -71,7 +70,7 @@
   @VisibleForTesting
   static final String PACKAGE_NAME_ERROR =
       "package names may contain A-Z, a-z, 0-9, or any of ' !\"#$%&'()*+,-./;<=>?[]^_`{|}~'"
-          + " (most 127-bit ascii characters except 0-31, 127, ':', '@', or '\\')";
+          + " (most 127-bit ascii characters except 0-31, 127, ':', or '\\')";
 
   @VisibleForTesting
   static final String PACKAGE_NAME_DOT_ERROR =
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
index 8d7ad19..732e6a0 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
@@ -16,6 +16,7 @@
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ComparisonChain;
+import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Interner;
 import com.google.devtools.build.lib.concurrent.BlazeInterners;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
@@ -119,10 +120,17 @@
   }
 
   public static PackageIdentifier parse(String input) throws LabelSyntaxException {
-    String repo;
+    return parse(input, /* repo= */ null, /* repositoryMapping= */ null);
+  }
+
+  public static PackageIdentifier parse(
+      String input, String repo, ImmutableMap<RepositoryName, RepositoryName> repositoryMapping)
+      throws LabelSyntaxException {
     String packageName;
     int packageStartPos = input.indexOf("//");
-    if (input.startsWith("@") && packageStartPos > 0) {
+    if (repo != null) {
+      packageName = input;
+    } else if (input.startsWith("@") && packageStartPos > 0) {
       repo = input.substring(0, packageStartPos);
       packageName = input.substring(packageStartPos + 2);
     } else if (input.startsWith("@")) {
@@ -145,7 +153,13 @@
       throw new LabelSyntaxException(error);
     }
 
-    return create(repo, PathFragment.create(packageName));
+    if (repositoryMapping != null) {
+      RepositoryName repositoryName = RepositoryName.create(repo);
+      repositoryName = repositoryMapping.getOrDefault(repositoryName, repositoryName);
+      return create(repositoryName, PathFragment.create(packageName));
+    } else {
+      return create(repo, PathFragment.create(packageName));
+    }
   }
 
   public RepositoryName getRepository() {