diff --git a/src/fits/GFitsTable.cpp b/src/fits/GFitsTable.cpp
index cac5447..fef35ac 100644
--- a/src/fits/GFitsTable.cpp
+++ b/src/fits/GFitsTable.cpp
@@ -265,17 +265,15 @@ GFitsTableCol& GFitsTable::operator[](const std::string& colname)
     // Initialise pointer
     GFitsTableCol* ptr = NULL;
 
-    // If there are columns then search for the specified name
-    if (m_columns != NULL) {
-        for (int i = 0; i < m_cols; ++i) {
-            if (m_columns[i]->name() == colname) {
-                ptr = m_columns[i];
-                if (ptr == NULL) {
-                    throw GException::fits_no_data(G_ACCESS2, 
-                                                   "No data for this column");
-                }
-                break;
+    // Search for the specified name
+    for (int i = 0; i < m_cols; ++i) {
+        if (m_columns[i]->name() == colname) {
+            ptr = m_columns[i];
+            if (ptr == NULL) {
+                throw GException::fits_no_data(G_ACCESS2, 
+                                               "No data for this column");
             }
+            break;
         }
     }
 
@@ -310,16 +308,14 @@ const GFitsTableCol& GFitsTable::operator[](const std::string& colname) const
     const GFitsTableCol* ptr = NULL;
 
     // If there are columns then search for the specified name
-    if (m_columns != NULL) {
-        for (int i = 0; i < m_cols; ++i) {
-            if (m_columns[i]->name() == colname) {
-                ptr = m_columns[i];
-                if (ptr == NULL) {
-                    throw GException::fits_no_data(G_ACCESS2, 
-                                                   "No data for this column");
-                }
-                break;
+    for (int i = 0; i < m_cols; ++i) {
+        if (m_columns[i]->name() == colname) {
+            ptr = m_columns[i];
+            if (ptr == NULL) {
+                throw GException::fits_no_data(G_ACCESS2, 
+                                               "No data for this column");
             }
+            break;
         }
     }
 
diff --git a/src/fits/GFitsTableStringCol.cpp b/src/fits/GFitsTableStringCol.cpp
index 8654e4b..5fe3b2b 100644
--- a/src/fits/GFitsTableStringCol.cpp
+++ b/src/fits/GFitsTableStringCol.cpp
@@ -183,7 +183,7 @@ std::string& GFitsTableStringCol::operator() (const int& row, const int& inx)
 const std::string& GFitsTableStringCol::operator() (const int& row, const int& inx) const
 {
     // If data are not available then load them now
-    if (m_data == NULL) ((GFitsTableStringCol*)this)->fetch_data();
+    if (m_data == NULL) fetch_data();
 
     // Return data bin
     return m_data[offset(row, inx)];
@@ -725,12 +725,12 @@ void GFitsTableStringCol::fetch_data(void) const
     m_size = m_number * m_length;
 
     // Free old buffer memory
-    const_cast<GFitsTableStringCol*>(this)->free_buffer();
+    free_buffer();
 
     // Allocate buffer memory
-    const_cast<GFitsTableStringCol*>(this)->alloc_buffer();
+    alloc_buffer();
 
-    // Save column
+    // Load column
     const_cast<GFitsTableStringCol*>(this)->load_column();
 
     // Extract string from buffer
@@ -740,7 +740,7 @@ void GFitsTableStringCol::fetch_data(void) const
     }
 
     // Free buffer memory
-    const_cast<GFitsTableStringCol*>(this)->free_buffer();
+    free_buffer();
 
     // Return
     return;
@@ -753,7 +753,7 @@ void GFitsTableStringCol::fetch_data(void) const
  * The CFITSIO transfer buffer allows transparent conversion from the CFITSIO
  * storage format to a vector of strings.
  ***************************************************************************/
-void GFitsTableStringCol::alloc_buffer(void)
+void GFitsTableStringCol::alloc_buffer(void) const
 {
     // Allocate buffer memory
     if (m_size > 0) {
@@ -780,7 +780,7 @@ void GFitsTableStringCol::alloc_buffer(void)
  *
  * Release memory that has been allocated for the CFITSIO transfer buffer.
  ***************************************************************************/
-void GFitsTableStringCol::free_buffer(void)
+void GFitsTableStringCol::free_buffer(void) const
 {
     // If there was a buffer allocated then free it
     if (m_buffer != NULL) {