diff --git a/common/bolt11.c b/common/bolt11.c
index bcc00cf38..bb3db5b04 100644
--- a/common/bolt11.c
+++ b/common/bolt11.c
@@ -833,6 +833,7 @@ struct bolt11 *bolt11_decode_nosig(const tal_t *ctx, const char *str,
 		 * anything except a `multiplier` (see table above)... MUST fail the
 		 * payment.
 		 **/
+		errno = 0;
 		amount = strtoull(amountstr, &end, 10);
 		if (amount == ULLONG_MAX && errno == ERANGE)
 			return decode_fail(b11, fail,
diff --git a/common/json_parse.c b/common/json_parse.c
index 1fb1fa97b..7b5c31c81 100644
--- a/common/json_parse.c
+++ b/common/json_parse.c
@@ -233,6 +233,7 @@ static void parse_number(const char **guide, u32 *number)
 	char *endp;
 	long int l;
 
+	errno = 0;
 	l = strtol(*guide, &endp, 10);
 	assert(endp != *guide);
 	assert(errno != ERANGE);
@@ -518,6 +519,7 @@ bool json_to_bitcoin_amount(const char *buffer, const jsmntok_t *tok,
 	char *end;
 	unsigned long btc, sat;
 
+	errno = 0;
 	btc = strtoul(buffer + tok->start, &end, 10);
 	if (btc == ULONG_MAX && errno == ERANGE)
 		return false;
diff --git a/common/json_parse_simple.c b/common/json_parse_simple.c
index a40cb02fb..0842fc58b 100644
--- a/common/json_parse_simple.c
+++ b/common/json_parse_simple.c
@@ -66,6 +66,7 @@ bool json_to_u64(const char *buffer, const jsmntok_t *tok, u64 *num)
 	char *end;
 	unsigned long long l;
 
+	errno = 0;
 	l = strtoull(buffer + tok->start, &end, 0);
 	if (end != buffer + tok->end)
 		return false;
@@ -88,6 +89,7 @@ bool json_to_s64(const char *buffer, const jsmntok_t *tok, s64 *num)
 	char *end;
 	long long l;
 
+	errno = 0;
 	l = strtoll(buffer + tok->start, &end, 0);
 	if (end != buffer + tok->end)
 		return false;
@@ -129,7 +131,7 @@ bool json_to_double(const char *buffer, const jsmntok_t *tok, double *num)
 	if (end != buffer + tok->end)
 		return false;
 
-	/* Check for overflow */
+	/* Check for overflow/underflow */
 	if (errno == ERANGE)
 		return false;