diff --git a/README.md b/README.md
index 29724d4..219be24 100644
--- a/README.md
+++ b/README.md
@@ -643,8 +643,8 @@ UTF-8 encoding of the given string.
 
 (**c-utf8->string** _c-bytevector_)
 
-Returns a newly allocated (unless empty) string whose character sequence is
-encoded by the given c-bytevector.
+Returns a newly allocated string whose character sequence is
+encoded by the given c-bytevector. It is an error if _c-bytevector_ is null.
 
 ### Utilities
 
diff --git a/foreign/c/pointer.scm b/foreign/c/pointer.scm
index eb5fc30..ed82702 100644
--- a/foreign/c/pointer.scm
+++ b/foreign/c/pointer.scm
@@ -76,6 +76,8 @@
 
 (define c-utf8->string
   (lambda (c-bytevector)
+    (when (c-null? c-bytevector)
+      (error "Can not turn null pointer into string"))
     (let ((size (c-strlen c-bytevector)))
       (utf8->string (c-bytevector->bytevector c-bytevector size)))))