diff --git a/icu4c/source/test/intltest/dcfmapts.cpp b/icu4c/source/test/intltest/dcfmapts.cpp
index 8a798dace9d..792385da664 100644
--- a/icu4c/source/test/intltest/dcfmapts.cpp
+++ b/icu4c/source/test/intltest/dcfmapts.cpp
@@ -26,11 +26,13 @@ void IntlTestDecimalFormatAPI::runIndexedTest( int32_t index, UBool exec, const
                 if (exec) {
                     logln((UnicodeString)"DecimalFormat API test---"); logln((UnicodeString)"");
                     UErrorCode status = U_ZERO_ERROR;
+                    Locale saveLocale;
                     Locale::setDefault(Locale::getEnglish(), status);
                     if(U_FAILURE(status)) {
                         errln((UnicodeString)"ERROR: Could not set default locale, test may not give correct results");
                     }
                     testAPI(/*par*/);
+                    Locale::setDefault(saveLocale, status);
                 }
                 break;
         case 1: name = "Rounding test";
diff --git a/icu4c/source/test/intltest/dtfmapts.cpp b/icu4c/source/test/intltest/dtfmapts.cpp
index 971213c2003..3c8fd4a6cab 100644
--- a/icu4c/source/test/intltest/dtfmapts.cpp
+++ b/icu4c/source/test/intltest/dtfmapts.cpp
@@ -29,11 +29,13 @@ void IntlTestDateFormatAPI::runIndexedTest( int32_t index, UBool exec, const cha
                 if (exec) {
                     logln("DateFormat API test---"); logln("");
                     UErrorCode status = U_ZERO_ERROR;
+                    Locale saveLocale;
                     Locale::setDefault(Locale::getEnglish(), status);
                     if(U_FAILURE(status)) {
                         errln("ERROR: Could not set default locale, test may not give correct results");
                     }
                     testAPI(/*par*/);
+                    Locale::setDefault(saveLocale, status);
                 }
                 break;
 
diff --git a/icu4c/source/test/intltest/intltest.cpp b/icu4c/source/test/intltest/intltest.cpp
index 7382f428324..8378b34a962 100644
--- a/icu4c/source/test/intltest/intltest.cpp
+++ b/icu4c/source/test/intltest/intltest.cpp
@@ -1136,6 +1136,8 @@ main(int argc, char* argv[])
         }
     }
 
+    Locale originalLocale;  // Save the default locale for comparison later on.
+
     /* TODO: Add option to call u_cleanup and rerun tests. */
     if (all) {
         major.runTest();
@@ -1172,12 +1174,17 @@ main(int argc, char* argv[])
     free(_testDataPath);
     _testDataPath = 0;
 
+    Locale lastDefaultLocale;
+    if (originalLocale != lastDefaultLocale) {
+        major.errln("FAILURE: A test changed the default locale without resetting it.");
+    }
+
     fprintf(stdout, "\n--------------------------------------\n");
     if (major.getErrors() == 0) {
         /* Call it twice to make sure that the defaults were reset. */
         /* Call it before the OK message to verify proper cleanup. */
         u_cleanup();
-     u_cleanup();
+        u_cleanup();
 
         fprintf(stdout, "OK: All tests passed without error.\n");
     }else{
diff --git a/icu4c/source/test/intltest/loctest.cpp b/icu4c/source/test/intltest/loctest.cpp
index 28348ccd5bb..f945fa6c0e8 100644
--- a/icu4c/source/test/intltest/loctest.cpp
+++ b/icu4c/source/test/intltest/loctest.cpp
@@ -1063,6 +1063,7 @@ LocaleTest::TestAtypicalLocales()
 
     int32_t i;
     UErrorCode status = U_ZERO_ERROR;
+    Locale saveLocale;
     Locale::setDefault(Locale::getUS(), status);
     for (i = 0; i < 9; ++i) {
         UnicodeString name;
@@ -1107,6 +1108,7 @@ LocaleTest::TestAtypicalLocales()
             errln("Lookup in Bengali failed: expected \"" + bengaliDisplayNames[i]
                         + "\", got \"" + name + "\"");
     }
+    Locale::setDefault(saveLocale, status);
 }
 
 #if !UCONFIG_NO_FORMATTING
@@ -1429,7 +1431,10 @@ LocaleTest::Test4147552()
                                                  "norsk (Noreg, NY)"
                                                  //"Norsk (Noreg, Nynorsk)"
     };
+    UErrorCode status = U_ZERO_ERROR;
 
+    Locale saveLocale;
+    Locale::setDefault(Locale::getEnglish(), status);
     for (int32_t i = 0; i < 3; ++i) {
         Locale loc = locales[i];
         UnicodeString temp;
@@ -1441,6 +1446,7 @@ LocaleTest::Test4147552()
                    norwegianDisplayNames[i] + ", got " +
                    loc.getDisplayName(loc, temp));
     }
+    Locale::setDefault(saveLocale, status);
 }
 
 void
diff --git a/icu4c/source/test/intltest/nmfmapts.cpp b/icu4c/source/test/intltest/nmfmapts.cpp
index 8d8875e02fc..e10998f2807 100644
--- a/icu4c/source/test/intltest/nmfmapts.cpp
+++ b/icu4c/source/test/intltest/nmfmapts.cpp
@@ -28,22 +28,26 @@ void IntlTestNumberFormatAPI::runIndexedTest( int32_t index, UBool exec, const c
                 if (exec) {
                     logln("NumberFormat API test---"); logln("");
                     UErrorCode status = U_ZERO_ERROR;
+                    Locale saveLocale;
                     Locale::setDefault(Locale::getEnglish(), status);
                     if(U_FAILURE(status)) {
                         errln("ERROR: Could not set default locale, test may not give correct results");
                     }
                     testAPI(/* par */);
+                    Locale::setDefault(saveLocale, status);
                 }
                 break;
         case 1: name = "NumberFormatRegistration"; 
                 if (exec) {
                     logln("NumberFormat Registration test---"); logln("");
                     UErrorCode status = U_ZERO_ERROR;
+                    Locale saveLocale;
                     Locale::setDefault(Locale::getEnglish(), status);
                     if(U_FAILURE(status)) {
                         errln("ERROR: Could not set default locale, test may not give correct results");
                     }
                     testRegistration();
+                    Locale::setDefault(saveLocale, status);
                 }
                 break;
         default: name = ""; break;
diff --git a/icu4c/source/test/intltest/sdtfmtts.cpp b/icu4c/source/test/intltest/sdtfmtts.cpp
index 15817d5d181..fafd375fb5a 100644
--- a/icu4c/source/test/intltest/sdtfmtts.cpp
+++ b/icu4c/source/test/intltest/sdtfmtts.cpp
@@ -26,11 +26,13 @@ void IntlTestSimpleDateFormatAPI::runIndexedTest( int32_t index, UBool exec, con
                 if (exec) {
                     logln("SimpleDateFormat API test---"); logln("");
                     UErrorCode status = U_ZERO_ERROR;
+                    Locale saveLocale;
                     Locale::setDefault(Locale::getEnglish(), status);
                     if(U_FAILURE(status)) {
                         errln("ERROR: Could not set default locale, test may not give correct results");
                     }
                     testAPI(/*par*/);
+                    Locale::setDefault(saveLocale, status);
                 }
                 break;