diff --git a/icu4c/source/common/mutex.cpp b/icu4c/source/common/mutex.cpp
index b2937e819f..fa2dbd0066 100644
--- a/icu4c/source/common/mutex.cpp
+++ b/icu4c/source/common/mutex.cpp
@@ -11,6 +11,13 @@
 /* Initialize the global mutex only when we can use it. */
 #if (ICU_USE_THREADS == 1)
 
+/*
+ * NOTE:  This function replicates functionality from the start
+ *        u_init().  Any changes must be made in both places.
+ *        TODO:  combine them.
+ *
+ *        This function runs only during C++ static initialization.
+ */
 static int GlobalMutexInitialize()
 {
     UErrorCode status = U_ZERO_ERROR;
diff --git a/icu4c/source/common/ucln_cmn.c b/icu4c/source/common/ucln_cmn.c
index 388b4a86d0..e74f3015fc 100644
--- a/icu4c/source/common/ucln_cmn.c
+++ b/icu4c/source/common/ucln_cmn.c
@@ -102,7 +102,12 @@ u_cleanup(void)
 
 U_CAPI void U_EXPORT2
 u_init(UErrorCode *status) {
-    /* Make sure the global mutex is initialized. */
+    /* Make sure the global mutexes are initialized. */
+    /*
+     * NOTE:  This section of code replicates functionality from GlobalMutexInitialize()
+     *        in the file mutex.cpp.  Any changes must be made in both places.
+     *        TODO:  combine them.
+     */
     umtx_init(NULL);
     ucnv_init(status);
     ures_init(status);