diff --git a/src/tools/pkcs11-tool.c b/src/tools/pkcs11-tool.c
index 6e774894..da8f53d4 100644
--- a/src/tools/pkcs11-tool.c
+++ b/src/tools/pkcs11-tool.c
@@ -750,7 +750,7 @@ get##ATTR(CK_SESSION_HANDLE sess, CK_OBJECT_HANDLE obj, CK_ULONG_PTR pulCount) \
  \
 	rv = p11->C_GetAttributeValue(sess, obj, &attr, 1); \
 	if (rv == CKR_OK) { \
-		if (!(attr.pValue = malloc(attr.ulValueLen))) \
+		if (!(attr.pValue = calloc(1, attr.ulValueLen + 1))) \
 			fatal("out of memory in get" #ATTR ": %m"); \
 		rv = p11->C_GetAttributeValue(sess, obj, &attr, 1); \
 	} \