diff --git a/icu4c/source/i18n/tzfmt.cpp b/icu4c/source/i18n/tzfmt.cpp
index 5aa7af5..cfde4ac 100644
--- a/icu4c/source/i18n/tzfmt.cpp
+++ b/icu4c/source/i18n/tzfmt.cpp
@@ -19,12 +19,15 @@
 #include "unicode/udat.h"
 #include "unicode/ustring.h"
 #include "unicode/utf16.h"
+#include "bytesinkutil.h"
+#include "charstr.h"
 #include "tzgnames.h"
 #include "cmemory.h"
 #include "cstring.h"
 #include "putilimp.h"
 #include "uassert.h"
 #include "ucln_in.h"
+#include "ulocimp.h"
 #include "umutex.h"
 #include "uresimp.h"
 #include "ureslocs.h"
@@ -327,10 +330,13 @@
     const char* region = fLocale.getCountry();
     int32_t regionLen = static_cast<int32_t>(uprv_strlen(region));
     if (regionLen == 0) {
-        char loc[ULOC_FULLNAME_CAPACITY];
-        uloc_addLikelySubtags(fLocale.getName(), loc, sizeof(loc), &status);
+        CharString loc;
+        {
+            CharStringByteSink sink(&loc);
+            ulocimp_addLikelySubtags(fLocale.getName(), sink, &status);
+        }
 
-        regionLen = uloc_getCountry(loc, fTargetRegion, sizeof(fTargetRegion), &status);
+        regionLen = uloc_getCountry(loc.data(), fTargetRegion, sizeof(fTargetRegion), &status);
         if (U_SUCCESS(status)) {
             fTargetRegion[regionLen] = 0;
         } else {
diff --git a/icu4c/source/i18n/tzgnames.cpp b/icu4c/source/i18n/tzgnames.cpp
index 4e3ecb4..8c0d4a2 100644
--- a/icu4c/source/i18n/tzgnames.cpp
+++ b/icu4c/source/i18n/tzgnames.cpp
@@ -21,12 +21,15 @@
 #include "unicode/strenum.h"
 #include "unicode/vtzone.h"
 
+#include "bytesinkutil.h"
+#include "charstr.h"
 #include "cmemory.h"
 #include "cstring.h"
 #include "mutex.h"
 #include "uhash.h"
 #include "uassert.h"
 #include "umutex.h"
+#include "ulocimp.h"
 #include "uresimp.h"
 #include "ureslocs.h"
 #include "zonemeta.h"
@@ -412,10 +415,13 @@
     const char* region = fLocale.getCountry();
     int32_t regionLen = static_cast<int32_t>(uprv_strlen(region));
     if (regionLen == 0) {
-        char loc[ULOC_FULLNAME_CAPACITY];
-        uloc_addLikelySubtags(fLocale.getName(), loc, sizeof(loc), &status);
+        CharString loc;
+        {
+            CharStringByteSink sink(&loc);
+            ulocimp_addLikelySubtags(fLocale.getName(), sink, &status);
+        }
 
-        regionLen = uloc_getCountry(loc, fTargetRegion, sizeof(fTargetRegion), &status);
+        regionLen = uloc_getCountry(loc.data(), fTargetRegion, sizeof(fTargetRegion), &status);
         if (U_SUCCESS(status)) {
             fTargetRegion[regionLen] = 0;
         } else {
diff --git a/icu4c/source/i18n/tznames_impl.cpp b/icu4c/source/i18n/tznames_impl.cpp
index 5e3b478..51d3e17 100644
--- a/icu4c/source/i18n/tznames_impl.cpp
+++ b/icu4c/source/i18n/tznames_impl.cpp
@@ -21,11 +21,14 @@
 #include "unicode/utf16.h"
 
 #include "tznames_impl.h"
+#include "bytesinkutil.h"
+#include "charstr.h"
 #include "cmemory.h"
 #include "cstring.h"
 #include "uassert.h"
 #include "mutex.h"
 #include "resource.h"
+#include "ulocimp.h"
 #include "uresimp.h"
 #include "ureslocs.h"
 #include "zonemeta.h"
@@ -2135,9 +2138,12 @@
     int32_t regionLen = static_cast<int32_t>(uprv_strlen(region));
     if (regionLen == 0) {
         UErrorCode status = U_ZERO_ERROR;
-        char loc[ULOC_FULLNAME_CAPACITY];
-        uloc_addLikelySubtags(fLocale.getName(), loc, sizeof(loc), &status);
-        regionLen = uloc_getCountry(loc, fRegion, sizeof(fRegion), &status);
+        CharString loc;
+        {
+            CharStringByteSink sink(&loc);
+            ulocimp_addLikelySubtags(fLocale.getName(), sink, &status);
+        }
+        regionLen = uloc_getCountry(loc.data(), fRegion, sizeof(fRegion), &status);
         if (U_SUCCESS(status) && regionLen < (int32_t)sizeof(fRegion)) {
             useWorld = FALSE;
         }