diff --git a/icu4c/source/common/loclikely.cpp b/icu4c/source/common/loclikely.cpp
index 737899e5b7a..f87fd8dd61c 100644
--- a/icu4c/source/common/loclikely.cpp
+++ b/icu4c/source/common/loclikely.cpp
@@ -300,6 +300,9 @@ ulocimp_addLikelySubtags(const char* localeID,
                          icu::ByteSink& sink,
                          UErrorCode& status) {
     if (U_FAILURE(status)) { return; }
+    if (localeID == nullptr) {
+        localeID = uloc_getDefault();
+    }
     icu::CharString localeBuffer = ulocimp_canonicalize(localeID, status);
     _uloc_addLikelySubtags(localeBuffer.data(), sink, status);
 }
@@ -334,6 +337,9 @@ ulocimp_minimizeSubtags(const char* localeID,
                         bool favorScript,
                         UErrorCode& status) {
     if (U_FAILURE(status)) { return; }
+    if (localeID == nullptr) {
+        localeID = uloc_getDefault();
+    }
     icu::CharString localeBuffer = ulocimp_canonicalize(localeID, status);
     _uloc_minimizeSubtags(localeBuffer.data(), sink, favorScript, status);
 }
diff --git a/icu4c/source/common/locresdata.cpp b/icu4c/source/common/locresdata.cpp
index 725e6609159..ba7163fa2db 100644
--- a/icu4c/source/common/locresdata.cpp
+++ b/icu4c/source/common/locresdata.cpp
@@ -161,6 +161,9 @@ _uloc_getOrientationHelper(const char* localeId,
 
     if (U_FAILURE(status)) { return result; }
 
+    if (localeId == nullptr) {
+        localeId = uloc_getDefault();
+    }
     icu::CharString localeBuffer = ulocimp_canonicalize(localeId, status);
 
     if (U_FAILURE(status)) { return result; }
diff --git a/icu4c/source/common/ucurr.cpp b/icu4c/source/common/ucurr.cpp
index db40f492c4c..cccf1130ae8 100644
--- a/icu4c/source/common/ucurr.cpp
+++ b/icu4c/source/common/ucurr.cpp
@@ -678,6 +678,9 @@ ucurr_getName(const char16_t* currency,
     // this function.
     UErrorCode ec2 = U_ZERO_ERROR;
 
+    if (locale == nullptr) {
+        locale = uloc_getDefault();
+    }
     CharString loc = ulocimp_getName(locale, ec2);
     if (U_FAILURE(ec2)) {
         *ec = U_ILLEGAL_ARGUMENT_ERROR;
@@ -776,6 +779,9 @@ ucurr_getPluralName(const char16_t* currency,
     // this function.
     UErrorCode ec2 = U_ZERO_ERROR;
 
+    if (locale == nullptr) {
+        locale = uloc_getDefault();
+    }
     CharString loc = ulocimp_getName(locale, ec2);
     if (U_FAILURE(ec2)) {
         *ec = U_ILLEGAL_ARGUMENT_ERROR;
@@ -969,6 +975,9 @@ collectCurrencyNames(const char* locale,
     // Look up the Currencies resource for the given locale.
     UErrorCode ec2 = U_ZERO_ERROR;
 
+    if (locale == nullptr) {
+        locale = uloc_getDefault();
+    }
     CharString loc = ulocimp_getName(locale, ec2);
     if (U_FAILURE(ec2)) {
         ec = U_ILLEGAL_ARGUMENT_ERROR;
diff --git a/icu4c/source/common/uloc.cpp b/icu4c/source/common/uloc.cpp
index 65a953da2cb..c69b021c94e 100644
--- a/icu4c/source/common/uloc.cpp
+++ b/icu4c/source/common/uloc.cpp
@@ -1824,9 +1824,6 @@ _canonicalize(const char* localeID,
         tempBuffer = ulocimp_forLanguageTag(localeIDPtr, -1, nullptr, err);
         tmpLocaleID = U_SUCCESS(err) && !tempBuffer.isEmpty() ? tempBuffer.data() : localeIDPtr;
     } else {
-        if (localeID==nullptr) {
-           localeID=uloc_getDefault();
-        }
         tmpLocaleID=localeID;
     }
 
@@ -2126,6 +2123,9 @@ uloc_getName(const char* localeID,
              int32_t nameCapacity,
              UErrorCode* err)
 {
+    if (localeID == nullptr) {
+        localeID = uloc_getDefault();
+    }
     return ByteSinkUtil::viaByteSinkToTerminatedChars(
         name, nameCapacity,
         [&](ByteSink& sink, UErrorCode& status) {
@@ -2159,6 +2159,9 @@ uloc_getBaseName(const char* localeID,
                  int32_t nameCapacity,
                  UErrorCode* err)
 {
+    if (localeID == nullptr) {
+        localeID = uloc_getDefault();
+    }
     return ByteSinkUtil::viaByteSinkToTerminatedChars(
         name, nameCapacity,
         [&](ByteSink& sink, UErrorCode& status) {
@@ -2192,6 +2195,9 @@ uloc_canonicalize(const char* localeID,
                   int32_t nameCapacity,
                   UErrorCode* err)
 {
+    if (localeID == nullptr) {
+        localeID = uloc_getDefault();
+    }
     return ByteSinkUtil::viaByteSinkToTerminatedChars(
         name, nameCapacity,
         [&](ByteSink& sink, UErrorCode& status) {
diff --git a/icu4c/source/common/uloc_tag.cpp b/icu4c/source/common/uloc_tag.cpp
index 4a5a83a6c54..b2e9946f48a 100644
--- a/icu4c/source/common/uloc_tag.cpp
+++ b/icu4c/source/common/uloc_tag.cpp
@@ -2596,6 +2596,9 @@ ulocimp_toLanguageTag(const char* localeID,
     bool hadPosix = false;
     const char* pKeywordStart;
 
+    if (localeID == nullptr) {
+        localeID = uloc_getDefault();
+    }
     /* Note: uloc_canonicalize returns "en_US_POSIX" for input locale ID "".  See #6835 */
     icu::CharString canonical = ulocimp_canonicalize(localeID, tmpStatus);
     if (U_FAILURE(tmpStatus)) {
diff --git a/icu4c/source/common/uresbund.cpp b/icu4c/source/common/uresbund.cpp
index 812e0dab9a3..afda2770fd3 100644
--- a/icu4c/source/common/uresbund.cpp
+++ b/icu4c/source/common/uresbund.cpp
@@ -2716,6 +2716,9 @@ ures_openWithType(UResourceBundle *r, const char* path, const char* localeID,
 
     UResourceDataEntry *entry;
     if(openType != URES_OPEN_DIRECT) {
+        if (localeID == nullptr) {
+            localeID = uloc_getDefault();
+        }
         /* first "canonicalize" the locale ID */
         CharString canonLocaleID = ulocimp_getBaseName(localeID, *status);
         if(U_FAILURE(*status)) {
@@ -3080,6 +3083,9 @@ ures_getFunctionalEquivalent(char *result, int32_t resultCapacity,
             kwVal.clear();
         }
     }
+    if (locid == nullptr) {
+        locid = uloc_getDefault();
+    }
     CharString base = ulocimp_getBaseName(locid, subStatus);
 #if defined(URES_TREE_DEBUG)
     fprintf(stderr, "getFunctionalEquivalent: \"%s\" [%s=%s] in %s - %s\n",