diff --git a/icu4c/source/test/cintltst/currtest.c b/icu4c/source/test/cintltst/currtest.c
index 0eba0f187af..330d5520f80 100644
--- a/icu4c/source/test/cintltst/currtest.c
+++ b/icu4c/source/test/cintltst/currtest.c
@@ -244,12 +244,13 @@ static const NumCodeTestEntry NUMCODE_TESTDATA[] = {
 };
 
 static void TestNumericCode(void) {
-    UChar code[4];
+    UChar code[8];  // at least one longer than the longest alphaCode
     int32_t i;
     int32_t numCode;
 
     for (i = 0; NUMCODE_TESTDATA[i].alphaCode; i++) {
-        u_charsToUChars(NUMCODE_TESTDATA[i].alphaCode, code, sizeof(code)/sizeof(code[0]));
+        int32_t length = uprv_strlen(NUMCODE_TESTDATA[i].alphaCode);
+        u_charsToUChars(NUMCODE_TESTDATA[i].alphaCode, code, length + 1);  // +1 includes the NUL
         numCode = ucurr_getNumericCode(code);
         if (numCode != NUMCODE_TESTDATA[i].numericCode) {
             log_data_err("Error: ucurr_getNumericCode returned %d for currency %s, expected - %d\n",