diff --git a/library/x509parse.c b/library/x509parse.c
index 535b180..0a3b6fe 100644
--- a/library/x509parse.c
+++ b/library/x509parse.c
@@ -1917,14 +1917,21 @@
 static int load_file( const char *path, unsigned char **buf, size_t *n )
 {
     FILE *f;
+    long size;
 
     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( POLARSSL_ERR_X509_FILE_IO_ERROR );
 
     fseek( f, 0, SEEK_END );
-    *n = (size_t) ftell( f );
+    if( ( size = ftell( f ) ) == -1 )
+    {
+        fclose( f );
+        return( POLARSSL_ERR_X509_FILE_IO_ERROR );
+    }
     fseek( f, 0, SEEK_SET );
 
+    *n = (size_t) size;
+
     if( *n + 1 == 0 ||
         ( *buf = (unsigned char *) polarssl_malloc( *n + 1 ) ) == NULL )
     {