diff --git a/icu4c/source/i18n/collationbuilder.h b/icu4c/source/i18n/collationbuilder.h
index a5fd8f427a42..f0c4df2b566f 100644
--- a/icu4c/source/i18n/collationbuilder.h
+++ b/icu4c/source/i18n/collationbuilder.h
@@ -180,26 +180,27 @@ class U_I18N_API CollationBuilder : public CollationRuleParser::Sink {
      *
      * The case bits are unused and available.
      */
-    static inline int64_t tempCEFromIndexAndStrength(int32_t index, int32_t strength) {
+    static inline uint64_t tempCEFromIndexAndStrength(int32_t index, int32_t strength) {
         return
             // CE byte offsets, to ensure valid CE bytes, and case bits 11
-            INT64_C(0x4040000006002000) +
+            UINT64_C(0x4040000006002000) +
             // index bits 19..13 -> primary byte 1 = CE bits 63..56 (byte values 40..BF)
-            (static_cast<int64_t>(index & 0xfe000) << 43) +
+            (static_cast<uint64_t>(index & 0xfe000) << 43) +
             // index bits 12..6 -> primary byte 2 = CE bits 55..48 (byte values 40..BF)
-            (static_cast<int64_t>(index & 0x1fc0) << 42) +
+            (static_cast<uint64_t>(index & 0x1fc0) << 42) +
             // index bits 5..0 -> secondary byte 1 = CE bits 31..24 (byte values 06..45)
             ((index & 0x3f) << 24) +
             // strength bits 1..0 -> tertiary byte 1 = CE bits 13..8 (byte values 20..23)
             (strength << 8);
     }
-    static inline int32_t indexFromTempCE(int64_t tempCE) {
-        tempCE -= INT64_C(0x4040000006002000);
+    static inline int32_t indexFromTempCE(uint64_t tempCE) {
+        tempCE -= UINT64_C(0x4040000006002000);
         return
             (static_cast<int32_t>(tempCE >> 43) & 0xfe000) |
             (static_cast<int32_t>(tempCE >> 42) & 0x1fc0) |
             (static_cast<int32_t>(tempCE >> 24) & 0x3f);
     }
+
     static inline int32_t strengthFromTempCE(int64_t tempCE) {
         return (static_cast<int32_t>(tempCE) >> 8) & 3;
     }
diff --git a/icu4c/source/test/intltest/regcoll.cpp b/icu4c/source/test/intltest/regcoll.cpp
index d401d625bb76..b44bc84c0f5c 100644
--- a/icu4c/source/test/intltest/regcoll.cpp
+++ b/icu4c/source/test/intltest/regcoll.cpp
@@ -1249,6 +1249,12 @@ void CollationRegressionTest::TestBeforeWithTooStrongAfter() {
     }
 }
 
+void CollationRegressionTest::TestICU23280IntOverFlow() {
+    UErrorCode status = U_ZERO_ERROR;
+    icu::LocalPointer<icu::RuleBasedCollator> col1(
+        new icu::RuleBasedCollator(u"&＠<*񏼠-󏼠 ", status));
+}
+
 void CollationRegressionTest::TestICU22555InfinityLoop() {
     char16_t data[] = {
         0x0020, 0x0026, 0x4000, 0x002c, 0x6601, 0x0106, 0xff7f, 0xff99,
@@ -1441,6 +1447,7 @@ void CollationRegressionTest::runIndexedTest(int32_t index, UBool exec, const ch
     TESTCASE_AUTO(TestICU22277);
     TESTCASE_AUTO(TestICU22517);
     TESTCASE_AUTO(TestICU22555InfinityLoop);
+    TESTCASE_AUTO(TestICU23280IntOverFlow);
     TESTCASE_AUTO_END;
 }
 
diff --git a/icu4c/source/test/intltest/regcoll.h b/icu4c/source/test/intltest/regcoll.h
index ab6575d5ecac..94e72b93032b 100644
--- a/icu4c/source/test/intltest/regcoll.h
+++ b/icu4c/source/test/intltest/regcoll.h
@@ -243,6 +243,7 @@ class CollationRegressionTest: public IntlTestCollator
     void TestICU22517();
 
     void TestICU22555InfinityLoop();
+    void TestICU23280IntOverFlow();
 
 private:
     //------------------------------------------------------------------------