diff --git a/icu4c/source/common/uchar_props_data.h b/icu4c/source/common/uchar_props_data.h
index 215afd1a525..2987d71a085 100644
--- a/icu4c/source/common/uchar_props_data.h
+++ b/icu4c/source/common/uchar_props_data.h
@@ -4257,6 +4257,6 @@ static const UCPTrie block_trie={
     0x0,
 };
 
-static const int32_t indexes[UPROPS_INDEX_COUNT]={0x2e8e,0x2e8e,0x2e8e,0x2e8e,0x6db4,3,0x86ce,0x87d5,0x8f67,0x8f67,0x50cf,0x2f75a31,0x152,0,0,0};
+static const int32_t indexes[UPROPS_INDEX_COUNT]={0x2e8e,0x2e8e,0x2e8e,0x2e8e,0x6db4,3,0x86ce,0x87d5,0x8f67,0x8f67,0x1d0cf,0x2f75a31,0x152,0,0,0};
 
 #endif  // INCLUDED_FROM_UCHAR_C
diff --git a/icu4c/source/common/unicode/uchar.h b/icu4c/source/common/unicode/uchar.h
index 82ec63ab524..a58540a8cc9 100644
--- a/icu4c/source/common/unicode/uchar.h
+++ b/icu4c/source/common/unicode/uchar.h
@@ -2763,6 +2763,15 @@ typedef enum UIndicConjunctBreak {
     U_INCB_EXTEND,
     /** @draft ICU 76 */
     U_INCB_LINKER,
+#ifndef U_HIDE_DEPRECATED_API
+    /**
+     * One more than the highest normal UIndicConjunctBreak value.
+     * The highest value is available via u_getIntPropertyMaxValue(UCHAR_INDIC_CONJUNCT_BREAK).
+     *
+     * @deprecated ICU 58 The numeric value may change over time, see ICU ticket #12420.
+     */
+    U_INCB_COUNT
+#endif  // U_HIDE_DEPRECATED_API
 } UIndicConjunctBreak;
 #endif  // U_HIDE_DRAFT_API
 
diff --git a/icu4c/source/data/in/uprops.icu b/icu4c/source/data/in/uprops.icu
index eb813e0a9d5..20c302d565e 100644
Binary files a/icu4c/source/data/in/uprops.icu and b/icu4c/source/data/in/uprops.icu differ
diff --git a/icu4c/source/test/cintltst/cucdtst.c b/icu4c/source/test/cintltst/cucdtst.c
index e278622dd29..854e8353451 100644
--- a/icu4c/source/test/cintltst/cucdtst.c
+++ b/icu4c/source/test/cintltst/cucdtst.c
@@ -2915,6 +2915,9 @@ TestAdditionalProperties(void) {
     if( u_getIntPropertyMaxValue(UCHAR_EAST_ASIAN_WIDTH) != (int32_t) (U_EA_COUNT -1)) {
         log_err("error: u_getIntPropertyMaxValue(UCHAR_EAST_ASIAN_WIDTH) wrong\n");
     }
+    if( u_getIntPropertyMaxValue(UCHAR_INDIC_CONJUNCT_BREAK) != (int32_t) (U_INCB_COUNT -1)) {
+        log_err("error: u_getIntPropertyMaxValue(UCHAR_INDIC_CONJUNCT_BREAK) wrong\n");
+    }
 
     /* test u_hasBinaryProperty() and u_getIntPropertyValue() */
     for(i=0; i<UPRV_LENGTHOF(props); ++i) {
diff --git a/tools/unicode/c/genprops/corepropsbuilder.cpp b/tools/unicode/c/genprops/corepropsbuilder.cpp
index 6e90e96e750..870774a55ce 100644
--- a/tools/unicode/c/genprops/corepropsbuilder.cpp
+++ b/tools/unicode/c/genprops/corepropsbuilder.cpp
@@ -965,6 +965,7 @@ CorePropsBuilder::build(UErrorCode &errorCode) {
     totalSize=4*offset;
 
     indexes[UPROPS_MAX_VALUES_INDEX]=
+        (((int32_t)U_INCB_COUNT-1)<<UPROPS_INCB_SHIFT)|
         (((int32_t)U_EA_COUNT-1)<<UPROPS_EA_SHIFT)|
         ((int32_t)USCRIPT_CODE_LIMIT-1);
     indexes[UPROPS_MAX_VALUES_2_INDEX]=