diff --git a/icu4c/source/common/uchar.c b/icu4c/source/common/uchar.c
index e5d03eb65e9..73f388175bd 100644
--- a/icu4c/source/common/uchar.c
+++ b/icu4c/source/common/uchar.c
@@ -65,7 +65,7 @@ getFoldingPropsOffset(uint32_t data) {
     }
 }
 
-static UBool
+static UBool U_CALLCONV
 isAcceptable(void *context,
              const char *type, const char *name,
              const UDataInfo *pInfo) {
diff --git a/icu4c/source/common/ucnv_bld.c b/icu4c/source/common/ucnv_bld.c
index 741df2d579d..5aea806c850 100644
--- a/icu4c/source/common/ucnv_bld.c
+++ b/icu4c/source/common/ucnv_bld.c
@@ -142,7 +142,7 @@ U_CAPI UBool U_EXPORT2 ucnv_cleanup(void) {
     return (SHARED_DATA_HASHTABLE == NULL);
 }
 
-static UBool
+static UBool U_CALLCONV
 isCnvAcceptable(void *context,
              const char *type, const char *name,
              const UDataInfo *pInfo) {
diff --git a/icu4c/source/common/ucnv_io.c b/icu4c/source/common/ucnv_io.c
index 2c525677449..40a0c72291c 100644
--- a/icu4c/source/common/ucnv_io.c
+++ b/icu4c/source/common/ucnv_io.c
@@ -179,7 +179,7 @@ static const char *defaultConverterName = NULL;
 #define GET_STRING(idx) (const char *)(stringTable + (idx))
 #define NUM_RESERVED_TAGS 2
 
-static UBool
+static UBool U_CALLCONV
 isAcceptable(void *context,
              const char *type, const char *name,
              const UDataInfo *pInfo) {
diff --git a/icu4c/source/common/unames.c b/icu4c/source/common/unames.c
index 4026e434162..a60e174fdf4 100644
--- a/icu4c/source/common/unames.c
+++ b/icu4c/source/common/unames.c
@@ -68,7 +68,7 @@ static UCharNames *uCharNames=NULL;
 static UBool
 isDataLoaded(UErrorCode *pErrorCode);
 
-static UBool
+static UBool U_CALLCONV
 isAcceptable(void *context,
              const char *type, const char *name,
              const UDataInfo *pInfo);
@@ -465,7 +465,7 @@ isDataLoaded(UErrorCode *pErrorCode) {
     return TRUE;
 }
 
-static UBool
+static UBool U_CALLCONV
 isAcceptable(void *context,
              const char *type, const char *name,
              const UDataInfo *pInfo) {
diff --git a/icu4c/source/common/unicode/ustring.h b/icu4c/source/common/unicode/ustring.h
index 89b2ae17891..22ee41a9b85 100644
--- a/icu4c/source/common/unicode/ustring.h
+++ b/icu4c/source/common/unicode/ustring.h
@@ -751,7 +751,7 @@ u_unescape(const char *src,
  * @stable
  */
 U_CDECL_BEGIN
-typedef UChar (*UNESCAPE_CHAR_AT)(int32_t offset, void *context);
+typedef UChar (U_CALLCONV *UNESCAPE_CHAR_AT)(int32_t offset, void *context);
 U_CDECL_END
 
 /**
diff --git a/icu4c/source/common/uresdata.c b/icu4c/source/common/uresdata.c
index b2624dfa51a..71600d55694 100644
--- a/icu4c/source/common/uresdata.c
+++ b/icu4c/source/common/uresdata.c
@@ -178,7 +178,7 @@ _res_findTableIndex(const Resource *pRoot, const Resource res, const char *key)
 
 /* helper for res_load() ---------------------------------------------------- */
 
-static UBool
+static UBool U_CALLCONV
 isAcceptable(void *context,
              const char *type, const char *name,
              const UDataInfo *pInfo) {
diff --git a/icu4c/source/common/ustring.c b/icu4c/source/common/ustring.c
index ba8e048050a..373b99c8e7d 100644
--- a/icu4c/source/common/ustring.c
+++ b/icu4c/source/common/ustring.c
@@ -1091,7 +1091,8 @@ u_unescapeAt(UNESCAPE_CHAR_AT charAt,
 }
 
 /* u_unescapeAt() callback to return a UChar from a char* */
-static UChar _charPtr_charAt(int32_t offset, void *context) {
+static UChar U_CALLCONV
+_charPtr_charAt(int32_t offset, void *context) {
     UChar c16;
     /* It would be more efficient to access the invariant tables
      * directly but there is no API for that. */
diff --git a/icu4c/source/extra/ustdio/loccache.c b/icu4c/source/extra/ustdio/loccache.c
index 3686a7c89f7..bf4b9ed74c4 100644
--- a/icu4c/source/extra/ustdio/loccache.c
+++ b/icu4c/source/extra/ustdio/loccache.c
@@ -26,7 +26,7 @@
 /* The global cache */
 UHashtable     *gLocaleCache = NULL;
 
-static U_EXPORT2 void U_CALLCONV
+static void U_CALLCONV
 hash_freeBundle(void* obj)
 {
     u_locbund_delete((ULocaleBundle *)obj);
diff --git a/icu4c/source/extra/ustdio/ustdio.c b/icu4c/source/extra/ustdio/ustdio.c
index 6d5b05fbb66..861e1cb6950 100644
--- a/icu4c/source/extra/ustdio/ustdio.c
+++ b/icu4c/source/extra/ustdio/ustdio.c
@@ -536,7 +536,8 @@ u_fgetc(UFILE        *f)
 }
 
 /* u_unescapeAt() callback to return a UChar from a UFILE */
-static UChar _charAt(int32_t offset, void *context) {
+static UChar U_CALLCONV
+_charAt(int32_t offset, void *context) {
     return ((UFILE*) context)->fUCPos[offset];
 }
 
diff --git a/icu4c/source/i18n/ucol_tok.cpp b/icu4c/source/i18n/ucol_tok.cpp
index 2be8faf7ff9..aa6380d3ecf 100644
--- a/icu4c/source/i18n/ucol_tok.cpp
+++ b/icu4c/source/i18n/ucol_tok.cpp
@@ -506,7 +506,7 @@ void ucol_uprv_tok_initData() {
   }
 }
 
-const UChar *
+U_CAPI const UChar * U_EXPORT2
 ucol_tok_getNextArgument(const UChar *start, const UChar *end, 
                                UColAttribute *attrib, UColAttributeValue *value, 
                                UErrorCode *status) {
diff --git a/icu4c/source/test/cintltst/cucdtst.c b/icu4c/source/test/cintltst/cucdtst.c
index e5ace45ad04..8f0a213d176 100644
--- a/icu4c/source/test/cintltst/cucdtst.c
+++ b/icu4c/source/test/cintltst/cucdtst.c
@@ -554,7 +554,7 @@ static void TestIdentifier()
  * Then it should check that the areas contain all the same properties except where overridden.
  * For this, it would have had to set a flag for which code points were listed explicitly.
  */
-static void
+static void U_CALLCONV
 unicodeDataLineFn(void *context,
                   char *fields[][2], int32_t fieldCount,
                   UErrorCode *pErrorCode)
diff --git a/icu4c/source/test/cintltst/nucnvtst.c b/icu4c/source/test/cintltst/nucnvtst.c
index b2181794852..707dabf0be1 100644
--- a/icu4c/source/test/cintltst/nucnvtst.c
+++ b/icu4c/source/test/cintltst/nucnvtst.c
@@ -3102,7 +3102,7 @@ static void TestConv(const uint16_t in[],int len, const char* conv, const char*
     free(cBuf);
     free(offsets);
 }
-static UChar
+static UChar U_CALLCONV
 _charAt(int32_t offset, void *context) {
     return ((char*)context)[offset];
 }
diff --git a/icu4c/source/test/cintltst/udatatst.c b/icu4c/source/test/cintltst/udatatst.c
index a6ad92e48c5..339e065958a 100644
--- a/icu4c/source/test/cintltst/udatatst.c
+++ b/icu4c/source/test/cintltst/udatatst.c
@@ -355,7 +355,7 @@ cleanupAndReturn:
 }
 
 
-static UBool
+static UBool U_CALLCONV
 isAcceptable1(void *context,
              const char *type, const char *name,
              const UDataInfo *pInfo) {
@@ -387,7 +387,7 @@ isAcceptable1(void *context,
     }
 }
 
-static UBool
+static UBool U_CALLCONV
 isAcceptable2(void *context, 
              const char *type, const char *name,
              const UDataInfo *pInfo){
@@ -411,7 +411,7 @@ isAcceptable2(void *context,
 
 
 }
-static UBool
+static UBool U_CALLCONV
 isAcceptable3(void *context, 
              const char *type, const char *name,
              const UDataInfo *pInfo){
@@ -483,7 +483,7 @@ static void TestUDataOpenChoiceDemo1() {
     }
 }
 
-static UBool
+static UBool U_CALLCONV
 isAcceptable(void *context, 
              const char *type, const char *name,
              const UDataInfo *pInfo){
diff --git a/icu4c/source/test/collperf/collperf.cpp b/icu4c/source/test/collperf/collperf.cpp
index 0851fcd6b39..7cc3783113b 100644
--- a/icu4c/source/test/collperf/collperf.cpp
+++ b/icu4c/source/test/collperf/collperf.cpp
@@ -483,7 +483,7 @@ void doBinarySearch()
         if (opt_strcmp || opt_strcmpCPO) 
         {
             unsigned long startTime = timeGetTime();
-            typedef int32_t (*PF)(const UChar *, const UChar *);
+            typedef int32_t (U_EXPORT2 *PF)(const UChar *, const UChar *);
             PF pf = u_strcmp;
             if (opt_strcmpCPO) {pf = u_strcmpCodePointOrder;}
             if (opt_strcmp && opt_win) {pf = (PF)wcscmp;}   // Damn the difference between int32_t and int
diff --git a/icu4c/source/tools/gennames/gennames.c b/icu4c/source/tools/gennames/gennames.c
index fdf81850154..e6714447fe3 100644
--- a/icu4c/source/tools/gennames/gennames.c
+++ b/icu4c/source/tools/gennames/gennames.c
@@ -354,7 +354,7 @@ init() {
 
 /* parsing ------------------------------------------------------------------ */
 
-static void
+static void U_CALLCONV
 lineFn(void *context,
        char *fields[][2], int32_t fieldCount,
        UErrorCode *pErrorCode) {
diff --git a/icu4c/source/tools/gennorm/gennorm.c b/icu4c/source/tools/gennorm/gennorm.c
index f147bd506c9..c187ce73eea 100644
--- a/icu4c/source/tools/gennorm/gennorm.c
+++ b/icu4c/source/tools/gennorm/gennorm.c
@@ -183,7 +183,7 @@ main(int argc, char* argv[]) {
 
 /* parser for DerivedNormalizationProperties.txt ---------------------------- */
 
-static void
+static void U_CALLCONV
 derivedNormalizationPropertiesLineFn(void *context,
                                      char *fields[][2], int32_t fieldCount,
                                      UErrorCode *pErrorCode) {
@@ -281,7 +281,7 @@ parseDerivedNormalizationProperties(const char *filename, UErrorCode *pErrorCode
 
 /* parser for UnicodeData.txt ----------------------------------------------- */
 
-static void
+static void U_CALLCONV
 unicodeDataLineFn(void *context,
                   char *fields[][2], int32_t fieldCount,
                   UErrorCode *pErrorCode) {
diff --git a/icu4c/source/tools/genprops/genprops.c b/icu4c/source/tools/genprops/genprops.c
index 7c6cdee708a..1322b8f3690 100644
--- a/icu4c/source/tools/genprops/genprops.c
+++ b/icu4c/source/tools/genprops/genprops.c
@@ -239,7 +239,7 @@ getTokenIndex(const char *const tokens[], int32_t countTokens, const char *s) {
 static uint32_t mirrorMappings[MAX_MIRROR_COUNT][2];
 static int32_t mirrorCount=0;
 
-static void
+static void U_CALLCONV
 mirrorLineFn(void *context,
              char *fields[][2], int32_t fieldCount,
              UErrorCode *pErrorCode) {
@@ -295,7 +295,7 @@ parseBidiMirroring(const char *filename, UErrorCode *pErrorCode) {
 static SpecialCasing specialCasings[MAX_SPECIAL_CASING_COUNT];
 static int32_t specialCasingCount=0;
 
-static void
+static void U_CALLCONV
 specialCasingLineFn(void *context,
                     char *fields[][2], int32_t fieldCount,
                     UErrorCode *pErrorCode) {
@@ -390,7 +390,7 @@ parseSpecialCasing(const char *filename, UErrorCode *pErrorCode) {
 static CaseFolding caseFoldings[MAX_CASE_FOLDING_COUNT];
 static int32_t caseFoldingCount=0;
 
-static void
+static void U_CALLCONV
 caseFoldingLineFn(void *context,
                   char *fields[][2], int32_t fieldCount,
                   UErrorCode *pErrorCode) {
@@ -546,7 +546,7 @@ static struct {
 
 static int32_t unicodeAreaIndex=0, mirrorIndex=0, specialCasingIndex=0, caseFoldingIndex=0;
 
-static void
+static void U_CALLCONV
 unicodeDataLineFn(void *context,
                   char *fields[][2], int32_t fieldCount,
                   UErrorCode *pErrorCode) {
diff --git a/icu4c/source/tools/genprops/props2.c b/icu4c/source/tools/genprops/props2.c
index 8c318bea09d..d30ee70c6b5 100644
--- a/icu4c/source/tools/genprops/props2.c
+++ b/icu4c/source/tools/genprops/props2.c
@@ -52,37 +52,37 @@ parseArabicShaping(char *filename, char *basename,
                    const char *suffix,
                    UErrorCode *pErrorCode);
 
-static void
+static void U_CALLCONV
 ageLineFn(void *context,
           char *fields[][2], int32_t fieldCount,
           UErrorCode *pErrorCode);
 
-static void
+static void U_CALLCONV
 scriptsLineFn(void *context,
               char *fields[][2], int32_t fieldCount,
               UErrorCode *pErrorCode);
 
-static void
+static void U_CALLCONV
 blocksLineFn(void *context,
              char *fields[][2], int32_t fieldCount,
              UErrorCode *pErrorCode);
 
-static void
+static void U_CALLCONV
 propListLineFn(void *context,
                char *fields[][2], int32_t fieldCount,
                UErrorCode *pErrorCode);
 
-static void
+static void U_CALLCONV
 derivedPropListLineFn(void *context,
                       char *fields[][2], int32_t fieldCount,
                       UErrorCode *pErrorCode);
 
-static void
+static void U_CALLCONV
 eaWidthLineFn(void *context,
               char *fields[][2], int32_t fieldCount,
               UErrorCode *pErrorCode);
 
-static void
+static void U_CALLCONV
 lineBreakLineFn(void *context,
                 char *fields[][2], int32_t fieldCount,
                 UErrorCode *pErrorCode);
@@ -191,7 +191,7 @@ parseTwoFieldFile(char *filename, char *basename,
 
 /* DerivedAge.txt ----------------------------------------------------------- */
 
-static void
+static void U_CALLCONV
 ageLineFn(void *context,
           char *fields[][2], int32_t fieldCount,
           UErrorCode *pErrorCode) {
@@ -235,7 +235,7 @@ ageLineFn(void *context,
 
 /* Scripts.txt -------------------------------------------------------------- */
 
-static void
+static void U_CALLCONV
 scriptsLineFn(void *context,
               char *fields[][2], int32_t fieldCount,
               UErrorCode *pErrorCode) {
@@ -394,7 +394,7 @@ blockNames[UBLOCK_COUNT]={
     "Supplementary Private Use Area-B"          /* 110 */
 };
 
-static void
+static void U_CALLCONV
 blocksLineFn(void *context,
              char *fields[][2], int32_t fieldCount,
              UErrorCode *pErrorCode) {
@@ -471,7 +471,7 @@ propListNames[]={
     "Logical_Order_Exception"
 };
 
-static void
+static void U_CALLCONV
 propListLineFn(void *context,
                char *fields[][2], int32_t fieldCount,
                UErrorCode *pErrorCode) {
@@ -509,7 +509,7 @@ derivedPropListNames[]={
     "XID_Continue"
 };
 
-static void
+static void U_CALLCONV
 derivedPropListLineFn(void *context,
                       char *fields[][2], int32_t fieldCount,
                       UErrorCode *pErrorCode) {
@@ -547,7 +547,7 @@ eaNames[U_EA_COUNT]={
     "W"         /* Wide, default for plane 2 */
 };
 
-static void
+static void U_CALLCONV
 eaWidthLineFn(void *context,
               char *fields[][2], int32_t fieldCount,
               UErrorCode *pErrorCode) {
@@ -619,7 +619,7 @@ lbNames[U_LB_COUNT]={
     "ZW"
 };
 
-static void
+static void U_CALLCONV
 lineBreakLineFn(void *context,
                 char *fields[][2], int32_t fieldCount,
                 UErrorCode *pErrorCode) {
@@ -715,7 +715,7 @@ jgNames[U_JG_COUNT]={
     "ZAIN"
 };
 
-static void
+static void U_CALLCONV
 arabicShapingLineFn(void *context,
                     char *fields[][2], int32_t fieldCount,
                     UErrorCode *pErrorCode) {
diff --git a/icu4c/source/tools/toolutil/ucbuf.c b/icu4c/source/tools/toolutil/ucbuf.c
index de410bd06b7..511f4dc163c 100644
--- a/icu4c/source/tools/toolutil/ucbuf.c
+++ b/icu4c/source/tools/toolutil/ucbuf.c
@@ -259,7 +259,7 @@ ucbuf_getc(UCHARBUF* buf,UErrorCode* err){
 
 
 /* u_unescapeAt() callback to return a UChar*/
-static UChar
+static UChar U_CALLCONV
 _charAt(int32_t offset, void *context) {
     return ((UCHARBUF*) context)->currentPos[offset];
 }