diff --git a/library/dhm.c b/library/dhm.c
index 92fd611..f09592a 100644
--- a/library/dhm.c
+++ b/library/dhm.c
@@ -422,7 +422,7 @@
     mbedtls_pem_init( &pem );
 
     /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
-    if( dhmin[dhminlen - 1] != '\0' )
+    if( dhminlen == 0 || dhmin[dhminlen - 1] != '\0' )
         ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
     else
         ret = mbedtls_pem_read_buffer( &pem,