diff --git a/src/cmi/scorm12_cmi.js b/src/cmi/scorm12_cmi.js
index 54dd312..60b02e4 100644
--- a/src/cmi/scorm12_cmi.js
+++ b/src/cmi/scorm12_cmi.js
@@ -516,7 +516,7 @@ class CMICore extends BaseCMI {
     let sessionTime = this.#session_time;
     const startTime = start_time;
 
-    if (typeof startTime !== 'undefined' || startTime === null) {
+    if (typeof startTime !== 'undefined' && startTime !== null) {
       const seconds = new Date().getTime() - startTime;
       sessionTime = Util.getSecondsAsHHMMSS(seconds / 1000);
     }
diff --git a/src/cmi/scorm2004_cmi.js b/src/cmi/scorm2004_cmi.js
index 2ab9413..f974040 100644
--- a/src/cmi/scorm2004_cmi.js
+++ b/src/cmi/scorm2004_cmi.js
@@ -480,7 +480,7 @@ export class CMI extends BaseCMI {
     let sessionTime = this.#session_time;
     const startTime = this.start_time;
 
-    if (typeof startTime !== 'undefined' || startTime === null) {
+    if (typeof startTime !== 'undefined' && startTime !== null) {
       const seconds = new Date().getTime() - startTime;
       sessionTime = Util.getSecondsAsISODuration(seconds / 1000);
     }