diff --git a/scripts/data_files/error.fmt b/scripts/data_files/error.fmt
index 5699d9e..0e128e8 100644
--- a/scripts/data_files/error.fmt
+++ b/scripts/data_files/error.fmt
@@ -44,9 +44,16 @@
 
 const char * mbedtls_high_level_strerr( int error_code )
 {
+    int high_level_error_code;
     const char *error_description = NULL;
 
-    switch( error_code )
+    if( error_code < 0 )
+        error_code = -error_code;
+
+    /* Extract the high-level part from the error code. */
+    high_level_error_code = error_code & 0xFF80;
+
+    switch( high_level_error_code )
     {
         /* Begin Auto-Generated Code. */
 HIGH_LEVEL_CODE_CHECKS
@@ -61,9 +68,16 @@
 
 const char * mbedtls_low_level_strerr( int error_code )
 {
+    int low_level_error_code;
     const char *error_description = NULL;
 
-    switch( error_code )
+    if( error_code < 0 )
+        error_code = -error_code;
+
+    /* Extract the low-level part from the error code. */
+    low_level_error_code = error_code & ~0xFF80;
+
+    switch( low_level_error_code )
     {
         /* Begin Auto-Generated Code. */
 LOW_LEVEL_CODE_CHECKS
@@ -96,7 +110,7 @@
         use_ret = ret & 0xFF80;
 
         // Translate high level error code.
-        high_level_error_description = mbedtls_high_level_strerr(use_ret);
+        high_level_error_description = mbedtls_high_level_strerr( ret );
 
         if( high_level_error_description == NULL )
             mbedtls_snprintf( buf, buflen, "UNKNOWN ERROR CODE (%04X)", use_ret );
@@ -133,7 +147,7 @@
     }
 
     // Translate low level error code.
-    low_level_error_description = mbedtls_low_level_strerr( use_ret );
+    low_level_error_description = mbedtls_low_level_strerr( ret );
 
     if( low_level_error_description == NULL )
         mbedtls_snprintf( buf, buflen, "UNKNOWN ERROR CODE (%04X)", use_ret );