Index: bin/sh/arith_yacc.h
===================================================================
--- bin/sh/arith_yacc.h
+++ bin/sh/arith_yacc.h
@@ -90,4 +90,5 @@
 
 extern union yystype yylval;
 
+arith_t strtoarith_t(const char *restrict nptr, char **restrict endptr);
 int yylex(void);
Index: bin/sh/arith_yacc.c
===================================================================
--- bin/sh/arith_yacc.c
+++ bin/sh/arith_yacc.c
@@ -104,7 +104,7 @@
 	if (str == NULL || *str == '\0')
 		str = "0";
 	errno = 0;
-	result = strtoarith_t(str, &p, 0);
+	result = strtoarith_t(str, &p);
 	if (errno != 0 || *p != '\0')
 		yyerror("variable conversion error");
 	return result;
Index: bin/sh/arith_yylex.c
===================================================================
--- bin/sh/arith_yylex.c
+++ bin/sh/arith_yylex.c
@@ -35,6 +35,8 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <ctype.h>
+#include <errno.h>
 #include <inttypes.h>
 #include <stdlib.h>
 #include <string.h>
@@ -50,6 +52,32 @@
 #error Arithmetic tokens are out of order.
 #endif
 
+arith_t
+strtoarith_t(const char *restrict nptr, char **restrict endptr)
+{
+	arith_t val;
+
+	while (isspace((unsigned char)*nptr))
+		nptr++;
+	switch (*nptr) {
+		case '-':
+			return strtoimax(nptr, endptr, 0);
+		case '0':
+			return (arith_t)strtoumax(nptr, endptr, 0);
+		default:
+			val = (arith_t)strtoumax(nptr, endptr, 0);
+			if (val >= 0)
+				return val;
+			else if (val == ARITH_MIN) {
+				errno = ERANGE;
+				return ARITH_MIN;
+			} else {
+				errno = ERANGE;
+				return ARITH_MAX;
+			}
+	}
+}
+
 int
 yylex(void)
 {
@@ -78,7 +106,7 @@
 		case '7':
 		case '8':
 		case '9':
-			yylval.val = strtoarith_t(buf, &end, 0);
+			yylval.val = strtoarith_t(buf, &end);
 			arith_buf = end;
 			return ARITH_NUM;
 		case 'A':
Index: bin/sh/shell.h
===================================================================
--- bin/sh/shell.h
+++ bin/sh/shell.h
@@ -59,7 +59,6 @@
  */
 typedef intmax_t arith_t;
 #define	ARITH_FORMAT_STR  "%" PRIdMAX
-#define	strtoarith_t(nptr, endptr, base)  (intmax_t)strtoumax(nptr, endptr, base)
 #define	ARITH_MIN INTMAX_MIN
 #define	ARITH_MAX INTMAX_MAX
 
Index: bin/sh/tests/expansion/Makefile
===================================================================
--- bin/sh/tests/expansion/Makefile
+++ bin/sh/tests/expansion/Makefile
@@ -22,6 +22,8 @@
 ${PACKAGE}FILES+=	arith13.0
 ${PACKAGE}FILES+=	arith14.0
 ${PACKAGE}FILES+=	arith15.0
+${PACKAGE}FILES+=	arith16.0
+${PACKAGE}FILES+=	arith17.0
 ${PACKAGE}FILES+=	assign1.0
 ${PACKAGE}FILES+=	cmdsubst1.0
 ${PACKAGE}FILES+=	cmdsubst2.0
Index: bin/sh/tests/expansion/arith16.0
===================================================================
--- bin/sh/tests/expansion/arith16.0
+++ bin/sh/tests/expansion/arith16.0
@@ -0,0 +1,26 @@
+# $FreeBSD$
+
+failures=0
+
+for x in \
+	0x10000000000000000 \
+	-0x8000000000000001 \
+	0xfffffffffffffffffffffffffffffffff \
+	-0xfffffffffffffffffffffffffffffffff \
+	02000000000000000000000 \
+	9223372036854775808 \
+	9223372036854775809 \
+	-9223372036854775809 \
+	9999999999999999999999999 \
+	-9999999999999999999999999
+do
+	msg=$({
+		v=$((x)) || :
+	} 3>&1 >&2 2>&3 3>&-)
+	r=$?
+	if [ "$r" = 0 ] || [ -z "$msg" ]; then
+		printf 'Failed: %s\n' "$x"
+		: $((failures += 1))
+	fi
+done
+exit $((failures > 0))
Index: bin/sh/tests/expansion/arith17.0
===================================================================
--- bin/sh/tests/expansion/arith17.0
+++ bin/sh/tests/expansion/arith17.0
@@ -0,0 +1,3 @@
+# $FreeBSD$
+
+[ $((9223372036854775809)) -gt 0 ]