diff --git a/lib/googleauth.rb b/lib/googleauth.rb
index 4abc0f7..f68f912 100644
--- a/lib/googleauth.rb
+++ b/lib/googleauth.rb
@@ -34,7 +34,7 @@ module Google
   # Module Auth provides classes that provide Google-specific authorization
   # used to access Google APIs.
   module Auth
-    NOT_FOUND = <<END
+    NOT_FOUND_ERROR = <<END
 Could not load the default credentials. Browse to
 https://developers.google.com/accounts/docs/application-default-credentials
 for more information
@@ -53,7 +53,7 @@ END
       return creds unless creds.nil?
       creds = ServiceAccountCredentials.from_well_known_path(scope)
       return creds unless creds.nil?
-      fail NOT_FOUND unless GCECredentials.on_gce?(options)
+      fail NOT_FOUND_ERROR unless GCECredentials.on_gce?(options)
       GCECredentials.new
     end
 
diff --git a/lib/googleauth/service_account.rb b/lib/googleauth/service_account.rb
index 2d26154..0cd841e 100644
--- a/lib/googleauth/service_account.rb
+++ b/lib/googleauth/service_account.rb
@@ -54,11 +54,11 @@ module Google
     # cf [Application Default Credentials](http://goo.gl/mkAHpZ)
     class ServiceAccountCredentials < Signet::OAuth2::Client
       ENV_VAR = 'GOOGLE_APPLICATION_CREDENTIALS'
-      NOT_FOUND_PREFIX =
+      NOT_FOUND_ERROR =
         "Unable to read the credential file specified by #{ENV_VAR}"
       TOKEN_CRED_URI = 'https://www.googleapis.com/oauth2/v3/token'
       WELL_KNOWN_PATH = 'gcloud/application_default_credentials.json'
-      WELL_KNOWN_PREFIX = 'Unable to read the default credential file'
+      WELL_KNOWN_ERROR = 'Unable to read the default credential file'
 
       class << self
         extend Memoist
@@ -79,7 +79,7 @@ module Google
           fail 'file #{path} does not exist' unless File.exist?(path)
           return new(scope, File.open(path))
         rescue StandardError => e
-          raise "#{NOT_FOUND_PREFIX}: #{e}"
+          raise "#{NOT_FOUND_ERROR}: #{e}"
         end
 
         # Creates an instance from a well known path.
@@ -94,7 +94,7 @@ module Google
           return nil unless File.exist?(path)
           return new(scope, File.open(path))
         rescue StandardError => e
-          raise "#{WELL_KNOWN_PREFIX}: #{e}"
+          raise "#{WELL_KNOWN_ERROR}: #{e}"
         end
       end