diff --git a/icu4c/source/test/intltest/testidn.cpp b/icu4c/source/test/intltest/testidn.cpp
index 96e4b7c06fa..844bef69cbb 100644
--- a/icu4c/source/test/intltest/testidn.cpp
+++ b/icu4c/source/test/intltest/testidn.cpp
@@ -104,7 +104,7 @@ static UOption options[]={
 
 extern int
 testData(TestIDNA& test) {
-    char filename[300];
+    char* filename = (char*) malloc(strlen(IntlTest::pathToDataDirectory())*3);
     //TODO get the srcDir dynamically 
     const char *srcDir=IntlTest::pathToDataDirectory(), *destDir=NULL, *suffix=NULL;
     char *basename=NULL;
@@ -178,6 +178,7 @@ testData(TestIDNA& test) {
 
     cleanup();
     pTestIDNA = NULL;
+    free(filename);
     return errorCode;
 }
 U_CDECL_BEGIN
diff --git a/icu4c/source/tools/genidna/genidna.c b/icu4c/source/tools/genidna/genidna.c
index 682f37870a9..855848df80a 100644
--- a/icu4c/source/tools/genidna/genidna.c
+++ b/icu4c/source/tools/genidna/genidna.c
@@ -88,7 +88,7 @@ static UOption options[]={
 
 extern int
 main(int argc, char* argv[]) {
-    char filename[300];
+    char* filename = NULL;
     const char *srcDir=NULL, *destDir=NULL, *suffix=NULL;
     char *basename=NULL;
     char *saveBasename = NULL;
@@ -147,7 +147,7 @@ main(int argc, char* argv[]) {
     }
 
     setUnicodeVersion(options[6].value);
-
+    filename = (char* ) uprv_malloc(uprv_strlen(srcDir) + 300); /* hopefully this should be enough */
     /* prepare the filename beginning with the source dir */
     if(uprv_strchr(srcDir,U_FILE_SEP_CHAR) == NULL){
         filename[0] = 0x2E;
@@ -240,6 +240,8 @@ main(int argc, char* argv[]) {
     if(printRules){
         printf("\t\t\"::[:AGE=3.2:]NFKC;\"\n\t}\n}");
     }
+
+    uprv_free(filename);
     return errorCode;
 }