diff --git a/core/math/expression.cpp b/core/math/expression.cpp
index b7fd26ae367..6d47fed1215 100644
--- a/core/math/expression.cpp
+++ b/core/math/expression.cpp
@@ -350,9 +350,9 @@ Error Expression::_get_token(Token &r_token) {
 							case READING_INT: {
 								if (is_digit(c)) {
 									if (is_first_char && c == '0') {
-										if (next_char == 'b') {
+										if (next_char == 'b' || next_char == 'B') {
 											reading = READING_BIN;
-										} else if (next_char == 'x') {
+										} else if (next_char == 'x' || next_char == 'X') {
 											reading = READING_HEX;
 										}
 									}
@@ -370,7 +370,7 @@ Error Expression::_get_token(Token &r_token) {
 							case READING_BIN: {
 								if (bin_beg && !is_binary_digit(c)) {
 									reading = READING_DONE;
-								} else if (c == 'b') {
+								} else if (c == 'b' || c == 'B') {
 									bin_beg = true;
 								}
 
@@ -378,7 +378,7 @@ Error Expression::_get_token(Token &r_token) {
 							case READING_HEX: {
 								if (hex_beg && !is_hex_digit(c)) {
 									reading = READING_DONE;
-								} else if (c == 'x') {
+								} else if (c == 'x' || c == 'X') {
 									hex_beg = true;
 								}
 
diff --git a/editor/import/resource_importer_imagefont.cpp b/editor/import/resource_importer_imagefont.cpp
index e0a8cd924b7..741287ece31 100644
--- a/editor/import/resource_importer_imagefont.cpp
+++ b/editor/import/resource_importer_imagefont.cpp
@@ -159,7 +159,7 @@ Error ResourceImporterImageFont::import(ResourceUID::ID p_source_id, const Strin
 								c++; // Skip "+".
 								continue;
 							}
-						} else if (range[c] == '0' && (c <= range.length() - 2) && range[c + 1] == 'x') {
+						} else if (range[c] == '0' && (c <= range.length() - 2) && (range[c + 1] == 'x' || range[c + 1] == 'X')) {
 							// Read hexadecimal value, start.
 							token = String();
 							if (step == STEP_START_BEGIN) {
diff --git a/modules/gdscript/editor/gdscript_highlighter.cpp b/modules/gdscript/editor/gdscript_highlighter.cpp
index 25e09504ce9..9d90c35736b 100644
--- a/modules/gdscript/editor/gdscript_highlighter.cpp
+++ b/modules/gdscript/editor/gdscript_highlighter.cpp
@@ -351,12 +351,12 @@ Dictionary GDScriptSyntaxHighlighter::_get_line_syntax_highlighting_impl(int p_l
 
 		// Special cases for numbers.
 		if (in_number && !is_a_digit) {
-			if (str[j] == 'b' && str[j - 1] == '0') {
+			if ((str[j] == 'b' || str[j] == 'B') && str[j - 1] == '0') {
 				is_bin_notation = true;
-			} else if (str[j] == 'x' && str[j - 1] == '0') {
+			} else if ((str[j] == 'x' || str[j] == 'X') && str[j - 1] == '0') {
 				is_hex_notation = true;
 			} else if (!((str[j] == '-' || str[j] == '+') && str[j - 1] == 'e' && !prev_is_digit) &&
-					!(str[j] == '_' && (prev_is_digit || str[j - 1] == 'b' || str[j - 1] == 'x' || str[j - 1] == '.')) &&
+					!(str[j] == '_' && (prev_is_digit || str[j - 1] == 'b' || str[j - 1] == 'B' || str[j - 1] == 'x' || str[j - 1] == 'X' || str[j - 1] == '.')) &&
 					!(str[j] == 'e' && (prev_is_digit || str[j - 1] == '_')) &&
 					!(str[j] == '.' && (prev_is_digit || (!prev_is_binary_op && (j > 0 && (str[j - 1] == '_' || str[j - 1] == '-' || str[j - 1] == '+' || str[j - 1] == '~'))))) &&
 					!((str[j] == '-' || str[j] == '+' || str[j] == '~') && !is_binary_op && !prev_is_binary_op && str[j - 1] != 'e')) {
diff --git a/modules/gdscript/gdscript_tokenizer.cpp b/modules/gdscript/gdscript_tokenizer.cpp
index dd936cbe7ed..2bc4b703e20 100644
--- a/modules/gdscript/gdscript_tokenizer.cpp
+++ b/modules/gdscript/gdscript_tokenizer.cpp
@@ -696,13 +696,13 @@ GDScriptTokenizer::Token GDScriptTokenizerText::number() {
 	if (_peek(-1) == '.') {
 		has_decimal = true;
 	} else if (_peek(-1) == '0') {
-		if (_peek() == 'x') {
+		if (_peek() == 'x' || _peek() == 'X') {
 			// Hexadecimal.
 			base = 16;
 			digit_check_func = is_hex_digit;
 			need_digits = true;
 			_advance();
-		} else if (_peek() == 'b') {
+		} else if (_peek() == 'b' || _peek() == 'B') {
 			// Binary.
 			base = 2;
 			digit_check_func = is_binary_digit;
diff --git a/modules/mono/glue/GodotSharp/GodotSharp/Core/StringExtensions.cs b/modules/mono/glue/GodotSharp/GodotSharp/Core/StringExtensions.cs
index c79c45fa08c..0ca2307e3db 100644
--- a/modules/mono/glue/GodotSharp/GodotSharp/Core/StringExtensions.cs
+++ b/modules/mono/glue/GodotSharp/GodotSharp/Core/StringExtensions.cs
@@ -979,7 +979,7 @@ namespace Godot
             {
                 if (instance.Length < 3)
                     return false;
-                if (instance[from] != '0' || instance[from + 1] != 'x')
+                if (instance[from] != '0' || instance[from + 1] != 'x' || instance[from + 1] != 'X')
                     return false;
                 from += 2;
             }
diff --git a/scene/resources/syntax_highlighter.cpp b/scene/resources/syntax_highlighter.cpp
index a2113a89e22..7905acfd0e4 100644
--- a/scene/resources/syntax_highlighter.cpp
+++ b/scene/resources/syntax_highlighter.cpp
@@ -302,12 +302,12 @@ Dictionary CodeHighlighter::_get_line_syntax_highlighting_impl(int p_line) {
 		}
 
 		// Check for dot or underscore or 'x' for hex notation in floating point number or 'e' for scientific notation.
-		if ((str[j] == '.' || str[j] == 'x' || str[j] == '_' || str[j] == 'f' || str[j] == 'e' || (uint_suffix_enabled && str[j] == 'u')) && !in_word && prev_is_number && !is_number) {
+		if ((str[j] == '.' || str[j] == 'x' || str[j] == 'X' || str[j] == '_' || str[j] == 'f' || str[j] == 'e' || (uint_suffix_enabled && str[j] == 'u')) && !in_word && prev_is_number && !is_number) {
 			is_number = true;
 			is_a_symbol = false;
 			is_char = false;
 
-			if (str[j] == 'x' && str[j - 1] == '0') {
+			if ((str[j] == 'x' || str[j] == 'X') && str[j - 1] == '0') {
 				is_hex_notation = true;
 			}
 		}
diff --git a/tests/core/math/test_expression.h b/tests/core/math/test_expression.h
index c3e42804919..8dbc5cae21a 100644
--- a/tests/core/math/test_expression.h
+++ b/tests/core/math/test_expression.h
@@ -213,6 +213,15 @@ TEST_CASE("[Expression] Underscored numeric literals") {
 	CHECK_MESSAGE(
 			expression.parse("0xff_99_00") == OK,
 			"The expression should parse successfully.");
+	CHECK_MESSAGE(
+			expression.parse("0Xff_99_00") == OK,
+			"The expression should parse successfully.");
+	CHECK_MESSAGE(
+			expression.parse("0b10_11_00") == OK,
+			"The expression should parse successfully.");
+	CHECK_MESSAGE(
+			expression.parse("0B10_11_00") == OK,
+			"The expression should parse successfully.");
 }
 
 TEST_CASE("[Expression] Built-in functions") {
diff --git a/tests/core/string/test_string.h b/tests/core/string/test_string.h
index ea60230947d..479f448f24d 100644
--- a/tests/core/string/test_string.h
+++ b/tests/core/string/test_string.h
@@ -545,7 +545,10 @@ TEST_CASE("[String] String to integer") {
 		CHECK(String(nums[i]).to_int() == num[i]);
 	}
 	CHECK(String("0b1011").to_int() == 1011); // Looks like a binary number, but to_int() handles this as a base-10 number, "b" is just ignored.
+	CHECK(String("0B1011").to_int() == 1011);
+
 	CHECK(String("0x1012").to_int() == 1012); // Looks like a hexadecimal number, but to_int() handles this as a base-10 number, "x" is just ignored.
+	CHECK(String("0X1012").to_int() == 1012);
 
 	ERR_PRINT_OFF
 	CHECK(String("999999999999999999999999999999999999999999999999999999999").to_int() == INT64_MAX); // Too large, largest possible is returned.
@@ -554,10 +557,10 @@ TEST_CASE("[String] String to integer") {
 }
 
 TEST_CASE("[String] Hex to integer") {
-	static const char *nums[12] = { "0xFFAE", "22", "0", "AADDAD", "0x7FFFFFFFFFFFFFFF", "-0xf", "", "000", "000f", "0xaA", "-ff", "-" };
-	static const int64_t num[12] = { 0xFFAE, 0x22, 0, 0xAADDAD, 0x7FFFFFFFFFFFFFFF, -0xf, 0, 0, 0xf, 0xaa, -0xff, 0x0 };
+	static const char *nums[13] = { "0xFFAE", "22", "0", "AADDAD", "0x7FFFFFFFFFFFFFFF", "-0xf", "", "000", "000f", "0xaA", "-ff", "-", "0XFFAE" };
+	static const int64_t num[13] = { 0xFFAE, 0x22, 0, 0xAADDAD, 0x7FFFFFFFFFFFFFFF, -0xf, 0, 0, 0xf, 0xaa, -0xff, 0x0, 0xFFAE };
 
-	for (int i = 0; i < 12; i++) {
+	for (int i = 0; i < 13; i++) {
 		CHECK(String(nums[i]).hex_to_int() == num[i]);
 	}
 
@@ -575,10 +578,10 @@ TEST_CASE("[String] Hex to integer") {
 }
 
 TEST_CASE("[String] Bin to integer") {
-	static const char *nums[10] = { "", "0", "0b0", "0b1", "0b", "1", "0b1010", "-0b11", "-1010", "0b0111111111111111111111111111111111111111111111111111111111111111" };
-	static const int64_t num[10] = { 0, 0, 0, 1, 0, 1, 10, -3, -10, 0x7FFFFFFFFFFFFFFF };
+	static const char *nums[11] = { "", "0", "0b0", "0b1", "0b", "1", "0b1010", "-0b11", "-1010", "0b0111111111111111111111111111111111111111111111111111111111111111", "0B1010" };
+	static const int64_t num[11] = { 0, 0, 0, 1, 0, 1, 10, -3, -10, 0x7FFFFFFFFFFFFFFF, 10 };
 
-	for (int i = 0; i < 10; i++) {
+	for (int i = 0; i < 11; i++) {
 		CHECK(String(nums[i]).bin_to_int() == num[i]);
 	}