diff --git a/deps/icu-small/source/common/unicode/utfiterator.h b/deps/icu-small/source/common/unicode/utfiterator.h
index 7e9fc4ba314d52..6e79a4403057ad 100644
--- a/deps/icu-small/source/common/unicode/utfiterator.h
+++ b/deps/icu-small/source/common/unicode/utfiterator.h
@@ -557,9 +557,11 @@ class UTFImpl<
 public:
     // Handle ill-formed UTF-8
     U_FORCE_INLINE static CP32 sub() {
-        switch (behavior) {
-            case UTF_BEHAVIOR_NEGATIVE: return U_SENTINEL;
-            case UTF_BEHAVIOR_FFFD: return 0xfffd;
+        if constexpr (behavior == UTF_BEHAVIOR_NEGATIVE) {
+            return U_SENTINEL;
+        } else {
+            static_assert(behavior == UTF_BEHAVIOR_FFFD);
+            return 0xfffd;
         }
     }
 
@@ -736,10 +738,13 @@ class UTFImpl<
 public:
     // Handle ill-formed UTF-16: One unpaired surrogate.
     U_FORCE_INLINE static CP32 sub(CP32 surrogate) {
-        switch (behavior) {
-            case UTF_BEHAVIOR_NEGATIVE: return U_SENTINEL;
-            case UTF_BEHAVIOR_FFFD: return 0xfffd;
-            case UTF_BEHAVIOR_SURROGATE: return surrogate;
+        if constexpr (behavior == UTF_BEHAVIOR_NEGATIVE) {
+            return U_SENTINEL;
+        } else if constexpr (behavior == UTF_BEHAVIOR_FFFD) {
+            return 0xfffd;
+        } else {
+            static_assert(behavior == UTF_BEHAVIOR_SURROGATE);
+            return surrogate;
         }
     }
 
@@ -822,10 +827,13 @@ class UTFImpl<
 public:
     // Handle ill-formed UTF-32
     U_FORCE_INLINE static CP32 sub(bool forSurrogate, CP32 surrogate) {
-        switch (behavior) {
-            case UTF_BEHAVIOR_NEGATIVE: return U_SENTINEL;
-            case UTF_BEHAVIOR_FFFD: return 0xfffd;
-            case UTF_BEHAVIOR_SURROGATE: return forSurrogate ? surrogate : 0xfffd;
+        if constexpr (behavior == UTF_BEHAVIOR_NEGATIVE) {
+            return U_SENTINEL;
+        } else if constexpr (behavior == UTF_BEHAVIOR_FFFD) {
+            return 0xfffd;
+        } else {
+            static_assert(behavior == UTF_BEHAVIOR_SURROGATE);
+            return forSurrogate ? surrogate : 0xfffd;
         }
     }
 
diff --git a/deps/icu-small/source/common/unicode/uvernum.h b/deps/icu-small/source/common/unicode/uvernum.h
index b5273a04fcf8d4..75acd4f0052a88 100644
--- a/deps/icu-small/source/common/unicode/uvernum.h
+++ b/deps/icu-small/source/common/unicode/uvernum.h
@@ -59,7 +59,7 @@
  *  This value will change in the subsequent releases of ICU
  *  @stable ICU 2.6
  */
-#define U_ICU_VERSION_MINOR_NUM 2
+#define U_ICU_VERSION_MINOR_NUM 3
 
 /** The current ICU patchlevel version as an integer.
  *  This value will change in the subsequent releases of ICU
@@ -132,7 +132,7 @@
  *  This value will change in the subsequent releases of ICU
  *  @stable ICU 2.4
  */
-#define U_ICU_VERSION "78.2"
+#define U_ICU_VERSION "78.3"
 
 /**
  * The current ICU library major version number as a string, for library name suffixes.
@@ -151,7 +151,7 @@
 /** Data version in ICU4C.
  * @internal ICU 4.4 Internal Use Only
  **/
-#define U_ICU_DATA_VERSION "78.2"
+#define U_ICU_DATA_VERSION "78.3"
 #endif  /* U_HIDE_INTERNAL_API */
 
 /*===========================================================================
diff --git a/deps/icu-small/source/data/in/icudt78l.dat.bz2 b/deps/icu-small/source/data/in/icudt78l.dat.bz2
index 5be75974fa3edd..21ca4cef1c2acd 100644
Binary files a/deps/icu-small/source/data/in/icudt78l.dat.bz2 and b/deps/icu-small/source/data/in/icudt78l.dat.bz2 differ
diff --git a/deps/icu-small/source/i18n/nfrule.cpp b/deps/icu-small/source/i18n/nfrule.cpp
index 26a6e818d5a9b2..3857f9f45f2e80 100644
--- a/deps/icu-small/source/i18n/nfrule.cpp
+++ b/deps/icu-small/source/i18n/nfrule.cpp
@@ -158,12 +158,17 @@ NFRule::makeRules(UnicodeString& description,
         UnicodeString sbuf;
         int32_t orElseOp = description.indexOf(gVerticalLine);
 
+        uint64_t mod = util64_pow(rule1->radix, rule1->exponent);
         // we'll actually only split the rule into two rules if its
         // base value is an even multiple of its divisor (or it's one
         // of the special rules)
+        if (rule1->baseValue > 0 && rule1->radix != 0 && mod == 0) {
+            status = U_NUMBER_ARG_OUTOFBOUNDS_ERROR;
+            return;
+        }
         if ((rule1->baseValue > 0
             && (rule1->radix != 0) // ICU-23109 Ensure next line won't "% 0"
-            && (rule1->baseValue % util64_pow(rule1->radix, rule1->exponent)) == 0)
+            && (rule1->baseValue % mod == 0))
             || rule1->getType() == kImproperFractionRule
             || rule1->getType() == kDefaultRule) {
 
diff --git a/tools/icu/current_ver.dep b/tools/icu/current_ver.dep
index e3f6a6100a73bb..3d923fec865aa2 100644
--- a/tools/icu/current_ver.dep
+++ b/tools/icu/current_ver.dep
@@ -1,6 +1,6 @@
 [
   {
-    "url": "https://github.com/unicode-org/icu/releases/download/release-78.2/icu4c-78.2-sources.tgz",
-    "md5": "2bf8db43ccdc837e402ac773f17c7cf8"
+    "url": "https://github.com/unicode-org/icu/releases/download/release-78.3/icu4c-78.3-sources.tgz",
+    "md5": "a7b736b570ef0e180c96a31715a00c78"
   }
 ]