diff --git a/icu4c/source/common/ucnv.cpp b/icu4c/source/common/ucnv.cpp
index 856be708785..5dcf35e0438 100644
--- a/icu4c/source/common/ucnv.cpp
+++ b/icu4c/source/common/ucnv.cpp
@@ -234,7 +234,7 @@ ucnv_safeClone(const UConverter* cnv, void *stackBuffer, int32_t *pBufferSize, U
         ptrdiff_t pointerAdjustment = aligned_p - p;
         if (bufferSizeNeeded + pointerAdjustment <= stackBufferSize) {
             stackBuffer = reinterpret_cast<void *>(aligned_p);
-            stackBufferSize -= pointerAdjustment;
+            stackBufferSize -= static_cast<int32_t>(pointerAdjustment);
         } else {
             /* prevent using the stack buffer but keep the size > 0 so that we do not just preflight */
             stackBufferSize = 1;
diff --git a/icu4c/source/tools/toolutil/pkg_genc.cpp b/icu4c/source/tools/toolutil/pkg_genc.cpp
index 3f71e00cb64..c98baaf0241 100644
--- a/icu4c/source/tools/toolutil/pkg_genc.cpp
+++ b/icu4c/source/tools/toolutil/pkg_genc.cpp
@@ -418,9 +418,9 @@ writeCCode(
         filename,
         destdir,
         buffer,
-        sizeof(buffer),
+        static_cast<int32_t>(sizeof(buffer)),
         entry + uprv_strlen(entry),
-        sizeof(entry) - uprv_strlen(entry),
+        static_cast<int32_t>(sizeof(entry) - uprv_strlen(entry)),
         ".c",
         optFilename);
 
@@ -679,7 +679,7 @@ getOutFilename(
         outFilenameBuilder.append(destdir, status);
         outFilenameBuilder.ensureEndsWithFileSeparator(status);
     } else {
-        outFilenameBuilder.append(inFilename, basename - inFilename, status);
+        outFilenameBuilder.append(inFilename, static_cast<int32_t>(basename - inFilename), status);
     }
     inFilename=basename;