diff --git a/CHANGELOG.md b/CHANGELOG.md
index 398424ea..6bd82b5f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -63,6 +63,8 @@ The git repositories are hosted at the following sites:
 
 ### Fixed
 
+* Fixed NULL handling in CharacterString sprintf which caused an endless
+  loop. (#1189)
 * Fixed a regression in the rpm_ack_object_property_process() function
   that prevented proper parsing of multi-object ReadPropertyMultiple ACK
   responses. The bug was introduced in PR [#765] and caused the function
diff --git a/src/bacnet/bacapp.c b/src/bacnet/bacapp.c
index 19a6984c..5588b8cb 100644
--- a/src/bacnet/bacapp.c
+++ b/src/bacnet/bacapp.c
@@ -2099,6 +2099,10 @@ int bacapp_snprintf_character_string(
                     retry with the next one. */
                 wclen = 1;
                 wc = L'?';
+            } else if (wclen == 0) {
+                /* Null wide character */
+                wc = L'.';
+                wclen = 1;
             } else {
                 if (!iswprint(wc)) {
                     wc = L'.';