--- a/toolkit/crashreporter/nsExceptionHandler.cpp
+++ b/toolkit/crashreporter/nsExceptionHandler.cpp
@@ -1108,17 +1108,17 @@ bool MinidumpCallback(
       OpenAPIData(apiData, descriptor.path());
 #else
       OpenAPIData(apiData, dump_path, minidump_id);
 #endif
       apiData.WriteBuffer(crashReporterAPIData->get(), crashReporterAPIData->Length());
     }
 
     if (currentSessionId) {
-      WriteAnnotation(apiData, "TelemetrySessionId", crashTimeString);
+      WriteAnnotation(apiData, "TelemetrySessionId", currentSessionId);
       WriteAnnotation(eventFile, "TelemetrySessionId", currentSessionId);
     }
 
     WriteAnnotation(apiData, "CrashTime", crashTimeString);
     WriteAnnotation(eventFile, "CrashTime", crashTimeString);
 
     WriteAnnotation(apiData, "UptimeTS", uptimeTSString);
     WriteAnnotation(eventFile, "UptimeTS", uptimeTSString);

--- a/toolkit/crashreporter/test/unit/test_crashreporter_crash.js
+++ b/toolkit/crashreporter/test/unit/test_crashreporter_crash.js
@@ -40,11 +40,15 @@ function run_test() {
              let scope = {};
              Components.utils.import("resource://gre/modules/TelemetryController.jsm", scope);
              scope.TelemetryController.testSetup();
            },
            function(mdump, extra) {
              do_check_eq(extra.TestKey, "TestValue");
              do_check_eq(extra["\u2665"], "\u{1F4A9}");
              do_check_eq(extra.Notes, "JunkMoreJunk");
-             do_check_true("TelemetrySessionId" in extra);
+             const UUID_REGEX = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
+             Assert.ok("TelemetrySessionId" in extra,
+                       "The TelemetrySessionId field is present in the extra file");
+             Assert.ok(UUID_REGEX.test(extra.TelemetrySessionId),
+                       "The TelemetrySessionId is a UUID");
            });
 }