--- a/toolkit/components/telemetry/TelemetryHistogram.cpp
+++ b/toolkit/components/telemetry/TelemetryHistogram.cpp
@@ -2807,17 +2807,17 @@ TelemetryHistogram::DeserializeHistogram
     // We can't even enumerate the processes in the loaded data, so
     // there is nothing we could recover from the persistence file. Bail out.
     JS_ClearPendingException(aCx);
     return NS_ERROR_FAILURE;
   }
 
   // Make sure we have enough storage for all the processes.
   PersistedHistogramStorage histogramsToUpdate;
-  if (!histogramsToUpdate.resize(processes.length())) {
+  if (!histogramsToUpdate.resize(static_cast<uint32_t>(ProcessID::Count))) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
   // The following block of code attempts to extract as much data as possible
   // from the serialized JSON, even in case of light data corruptions: if, for example,
   // the data for a single process is corrupted or is in an unexpected form, we press on
   // and attempt to load the data for the other processes.
   JS::RootedId process(aCx);
@@ -2963,17 +2963,17 @@ TelemetryHistogram::DeserializeKeyedHist
     // We can't even enumerate the processes in the loaded data, so
     // there is nothing we could recover from the persistence file. Bail out.
     JS_ClearPendingException(aCx);
     return NS_ERROR_FAILURE;
   }
 
   // Make sure we have enough storage for all the processes.
   PersistedKeyedHistogramStorage histogramsToUpdate;
-  if (!histogramsToUpdate.resize(processes.length())) {
+  if (!histogramsToUpdate.resize(static_cast<uint32_t>(ProcessID::Count))) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
   // The following block of code attempts to extract as much data as possible
   // from the serialized JSON, even in case of light data corruptions: if, for example,
   // the data for a single process is corrupted or is in an unexpected form, we press on
   // and attempt to load the data for the other processes.
   JS::RootedId process(aCx);