diff --git a/include/GFilename.hpp b/include/GFilename.hpp
index 585586b..a25edbc 100644
--- a/include/GFilename.hpp
+++ b/include/GFilename.hpp
@@ -61,8 +61,8 @@ public:
     int                length(void) const;
     const std::string& filename(void) const;
     std::string        extname(const std::string& defaultname = "") const;
-    int         extno(const int& defaultextno = 1) const;
-    int         extver(const int& defaultextver = 1) const;
+    int                extno(const int& defaultno = -1) const;
+    int                extver(const int& defaultver = 0) const;
     bool               has_extname(void) const;
     bool               has_extno(void) const;
     bool               has_extver(void) const;
@@ -77,7 +77,7 @@ protected:
 
     // Protected members
     std::string m_filename;  //!< Filename (with stripped extension info)
-    std::string m_extname;   //!< Extension name
+    std::string m_extname;   //!< Extension name ("": not set)
     int         m_extno;     //!< Extension number  (-1: not set)
     int         m_extver;    //!< Extension version (0: not set)
 };
diff --git a/pyext/GFilename.i b/pyext/GFilename.i
index f23966d..312310a 100644
--- a/pyext/GFilename.i
+++ b/pyext/GFilename.i
@@ -53,8 +53,8 @@ public:
     int                length(void) const;
     const std::string& filename(void) const;
     std::string        extname(const std::string& defaultname = "") const;
-    int                extno(const int& defaultextno = 1) const;
-    int                extver(const int& defaultextver = 1) const;
+    int                extno(const int& defaultno = -1) const;
+    int                extver(const int& defaultver = 0) const;
     bool               has_extname(void) const;
     bool               has_extno(void) const;
     bool               has_extver(void) const;
diff --git a/src/support/GFilename.cpp b/src/support/GFilename.cpp
index fa42d77..97ed953 100644
--- a/src/support/GFilename.cpp
+++ b/src/support/GFilename.cpp
@@ -227,21 +227,21 @@ std::string GFilename::extname(const std::string& defaultname) const
 /***********************************************************************//**
  * @brief Return extension number
  *
- * @param[in] defaultextno Default extension number (default: 1).
+ * @param[in] defaultno Default extension number (default: -11).
  * @return Integer containing extension number.
  *
  * Returns the extension number. If no extension number is given the number
- * provided by the @p defaultextno argument will be used. By default, the
- * @p defaultextno parameter is set to 1.
+ * provided by the @p defaultno argument will be used. By default, the
+ * @p defaultno parameter is set to -1.
  ***************************************************************************/
-int GFilename::extno(const int& defaultextno) const
+int GFilename::extno(const int& defaultno) const
 {
     // Set the extension number
     int extno = m_extno;
 
     // If no extension number is set, the use the default extension number
     if (!has_extno()) {
-        extno = defaultextno;
+        extno = defaultno;
     }
 
     // Return extension number
@@ -252,29 +252,28 @@ int GFilename::extno(const int& defaultextno) const
 /***********************************************************************//**
  * @brief Return extension version number
  *
- * @param[in] defaultextver Default extension version number (default: 1).
+ * @param[in] defaultver Default extension version number (default: 0).
  * @return Integer containing extension version number.
  *
- * Returns the extension version number. If no extension version number is given the number
- * provided by the @p defaultextver argument will be used. By default, the
- * @p defaultextver parameter is set to 1.
+ * Returns the extension version number. If no extension version number is
+ * given the number provided by the @p defaultver argument will be used. By
+ * default, the @p defaultextver parameter is set to 0.
  ***************************************************************************/
-int GFilename::extver(const int& defaultextver) const
+int GFilename::extver(const int& defaultver) const
 {
-    // Set the extension version number
+    // Set the extension version
     int extver = m_extver;
 
-    // If no extension number is set, the use the default extension version number
+    // If no extension version is set, the use the default extension version
     if (!has_extver()) {
-        extver = defaultextver;
+        extver = defaultver;
     }
 
-    // Return extension number
+    // Return extension version
     return (extver);
 }
 
 
-
 /***********************************************************************//**
  * @brief Print file name information
  *
diff --git a/test/test_GSupport.cpp b/test/test_GSupport.cpp
index a8de738..d58fc6b 100644
--- a/test/test_GSupport.cpp
+++ b/test/test_GSupport.cpp
@@ -768,6 +768,18 @@ void TestGSupport::test_filename(void)
                 "Expected \"LUCKY\" extension name, "
                 "found \""+filename.extname()+"\"");
 
+    // Test default extension number
+    filename = "myfile.fits";
+    test_value(filename.extno(1), 1);
+    filename = "myfile.fits[3]";
+    test_value(filename.extno(1), 3);
+
+    // Test default extension version
+    filename = "myfile.fits";
+    test_value(filename.extver(1), 1);
+    filename = "myfile.fits[3,3]";
+    test_value(filename.extver(1), 3);
+
     // Return
     return;
 }