diff --git a/icu4c/source/common/pos2.h b/icu4c/source/common/pos2.h
index 766bef87518..450eb819d28 100644
--- a/icu4c/source/common/pos2.h
+++ b/icu4c/source/common/pos2.h
@@ -37,6 +37,9 @@
 #define HAVE_UINT32_T 0
 #define HAVE_BOOL_T 0
 
+/* Determines the endianness of the platform */
+#define U_IS_BIG_ENDIAN 0
+
 /*===========================================================================*/
 /* Generic data types                                                        */
 /*===========================================================================*/
diff --git a/icu4c/source/common/pos400.h b/icu4c/source/common/pos400.h
index 7361b5586ca..c72a89f6b66 100644
--- a/icu4c/source/common/pos400.h
+++ b/icu4c/source/common/pos400.h
@@ -38,6 +38,9 @@
 #define HAVE_UINT32_T 0
 #define HAVE_BOOL_T 0
 
+/* Determines the endianness of the platform */
+#define U_IS_BIG_ENDIAN 1
+
 /*===========================================================================*/
 /* Generic data types                                                        */
 /*===========================================================================*/
diff --git a/icu4c/source/common/pwin32.h b/icu4c/source/common/pwin32.h
index 1d6fea74ff4..72f6fd97d1d 100644
--- a/icu4c/source/common/pwin32.h
+++ b/icu4c/source/common/pwin32.h
@@ -37,6 +37,9 @@
 #define HAVE_UINT32_T 0
 #define HAVE_BOOL_T 0
 
+/* Determines the endianness of the platform */
+#define U_IS_BIG_ENDIAN 0
+
 /*===========================================================================*/
 /* Generic data types                                                        */
 /*===========================================================================*/