diff --git a/ext/gmp/gmp.c b/ext/gmp/gmp.c
index 4894b09afe442..b6329daeeea0e 100644
--- a/ext/gmp/gmp.c
+++ b/ext/gmp/gmp.c
@@ -586,6 +586,33 @@ ZEND_MODULE_INFO_D(gmp)
 }
 /* }}} */
 
+static zend_result convert_zstr_to_gmp(mpz_t gmp_number, const zend_string *val, zend_long base, uint32_t arg_pos)
+{
+	const char *num_str = ZSTR_VAL(val);
+	bool skip_lead = false;
+
+	if (ZSTR_LEN(val) >= 2 && num_str[0] == '0') {
+		if ((base == 0 || base == 16) && (num_str[1] == 'x' || num_str[1] == 'X')) {
+			base = 16;
+			skip_lead = true;
+		} else if ((base == 0 || base == 2) && (num_str[1] == 'b' || num_str[1] == 'B')) {
+			base = 2;
+			skip_lead = true;
+		}
+	}
+
+	int gmp_ret = mpz_set_str(gmp_number, (skip_lead ? &num_str[2] : num_str), (int) base);
+	if (-1 == gmp_ret) {
+		if (arg_pos == 0) {
+			zend_value_error("Number is not an integer string");
+		} else {
+			zend_argument_value_error(arg_pos, "is not an integer string");
+		}
+		return FAILURE;
+	}
+
+	return SUCCESS;
+}
 
 /* {{{ convert_to_gmp
  * Convert zval to be gmp number */
@@ -596,31 +623,7 @@ static zend_result convert_to_gmp(mpz_t gmpnumber, zval *val, zend_long base, ui
 		mpz_set_si(gmpnumber, Z_LVAL_P(val));
 		return SUCCESS;
 	case IS_STRING: {
-		char *numstr = Z_STRVAL_P(val);
-		zend_bool skip_lead = 0;
-		int ret;
-
-		if (Z_STRLEN_P(val) >= 2 && numstr[0] == '0') {
-			if ((base == 0 || base == 16) && (numstr[1] == 'x' || numstr[1] == 'X')) {
-				base = 16;
-				skip_lead = 1;
-			} else if ((base == 0 || base == 2) && (numstr[1] == 'b' || numstr[1] == 'B')) {
-				base = 2;
-				skip_lead = 1;
-			}
-		}
-
-		ret = mpz_set_str(gmpnumber, (skip_lead ? &numstr[2] : numstr), (int) base);
-		if (-1 == ret) {
-			if (arg_pos == 0) {
-				zend_value_error("Number is not an integer string");
-			} else {
-				zend_argument_value_error(arg_pos, "is not an integer string");
-			}
-			return FAILURE;
-		}
-
-		return SUCCESS;
+		return convert_zstr_to_gmp(gmpnumber, Z_STR_P(val), base, arg_pos);
 	}
 	default: {
 		zend_long lval;
@@ -868,22 +871,29 @@ static inline void _gmp_unary_opl(INTERNAL_FUNCTION_PARAMETERS, gmp_unary_opl_t
 /* {{{ Initializes GMP number */
 ZEND_FUNCTION(gmp_init)
 {
-	zval *number_arg;
-	mpz_ptr gmpnumber;
+	mpz_ptr gmp_number;
+	zend_string *arg_str = NULL;
+	zend_long arg_l = 0;
 	zend_long base = 0;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "z|l", &number_arg, &base) == FAILURE) {
-		RETURN_THROWS();
-	}
+	ZEND_PARSE_PARAMETERS_START(1, 2)
+		Z_PARAM_STR_OR_LONG(arg_str, arg_l)
+		Z_PARAM_OPTIONAL
+		Z_PARAM_LONG(base)
+	ZEND_PARSE_PARAMETERS_END();
 
 	if (base && (base < 2 || base > GMP_MAX_BASE)) {
 		zend_argument_value_error(2, "must be between 2 and %d", GMP_MAX_BASE);
 		RETURN_THROWS();
 	}
 
-	INIT_GMP_RETVAL(gmpnumber);
-	if (convert_to_gmp(gmpnumber, number_arg, base, 1) == FAILURE) {
-		RETURN_THROWS();
+	INIT_GMP_RETVAL(gmp_number);
+	if (arg_str) {
+		if (convert_zstr_to_gmp(gmp_number, arg_str, base, 1) == FAILURE) {
+			RETURN_THROWS();
+		}
+	} else {
+		mpz_set_si(gmp_number, arg_l);
 	}
 }
 /* }}} */
diff --git a/ext/gmp/tests/gh9308.phpt b/ext/gmp/tests/gh9308.phpt
new file mode 100644
index 0000000000000..1634308d805e0
--- /dev/null
+++ b/ext/gmp/tests/gh9308.phpt
@@ -0,0 +1,19 @@
+--TEST--
+Bug GH-9308: GMP throws the wrong error when a GMP object is passed to gmp_init()
+--SKIPIF--
+<?php if (!extension_loaded("gmp")) print "skip"; ?>
+--FILE--
+<?php
+declare(strict_types=1);
+
+/* We need strict_types as GMP has a __toString() handler */
+
+try {
+    $gmp = gmp_init(gmp_init(123));
+} catch (\TypeError $e) {
+    echo $e->getMessage(), \PHP_EOL;
+}
+
+?>
+--EXPECT--
+gmp_init(): Argument #1 ($num) must be of type string|int, GMP given