diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c
index f185e24601cb..2c136bacb1a8 100644
--- a/cmd/zdb/zdb.c
+++ b/cmd/zdb/zdb.c
@@ -8800,7 +8800,7 @@ zdb_read_block(char *thing, spa_t *spa)
 	void *lbuf, *buf;
 	char *s, *p, *dup, *flagstr, *sizes, *tmp = NULL;
 	const char *vdev, *errmsg = NULL;
-	int i, error;
+	int i, len, error;
 	boolean_t borrowed = B_FALSE, found = B_FALSE;
 
 	dup = strdup(thing);
@@ -8828,7 +8828,8 @@ zdb_read_block(char *thing, spa_t *spa)
 	for (s = strtok_r(flagstr, ":", &tmp);
 	    s != NULL;
 	    s = strtok_r(NULL, ":", &tmp)) {
-		for (i = 0; i < strlen(flagstr); i++) {
+		len = strlen(flagstr);
+		for (i = 0; i < len; i++) {
 			int bit = flagbits[(uchar_t)flagstr[i]];
 
 			if (bit == 0) {
@@ -9098,13 +9099,14 @@ zdb_embedded_block(char *thing)
 static boolean_t
 zdb_numeric(char *str)
 {
-	int i = 0;
+	int i = 0, len;
 
-	if (strlen(str) == 0)
+	len = strlen(str);
+	if (len == 0)
 		return (B_FALSE);
 	if (strncmp(str, "0x", 2) == 0 || strncmp(str, "0X", 2) == 0)
 		i = 2;
-	for (; i < strlen(str); i++) {
+	for (; i < len; i++) {
 		if (!isxdigit(str[i]))
 			return (B_FALSE);
 	}
diff --git a/cmd/ztest.c b/cmd/ztest.c
index c58d35c9909c..523f280aae1a 100644
--- a/cmd/ztest.c
+++ b/cmd/ztest.c
@@ -685,15 +685,17 @@ static int
 str2shift(const char *buf)
 {
 	const char *ends = "BKMGTPEZ";
-	int i;
+	int i, len;
 
 	if (buf[0] == '\0')
 		return (0);
-	for (i = 0; i < strlen(ends); i++) {
+
+	len = strlen(ends);
+	for (i = 0; i < len; i++) {
 		if (toupper(buf[0]) == ends[i])
 			break;
 	}
-	if (i == strlen(ends)) {
+	if (i == len) {
 		(void) fprintf(stderr, "ztest: invalid bytes suffix: %s\n",
 		    buf);
 		usage(B_FALSE);
diff --git a/lib/libzfs/libzfs_util.c b/lib/libzfs/libzfs_util.c
index cba071a1a900..1f7e7b0e647e 100644
--- a/lib/libzfs/libzfs_util.c
+++ b/lib/libzfs/libzfs_util.c
@@ -1618,15 +1618,17 @@ static int
 str2shift(libzfs_handle_t *hdl, const char *buf)
 {
 	const char *ends = "BKMGTPEZ";
-	int i;
+	int i, len;
 
 	if (buf[0] == '\0')
 		return (0);
-	for (i = 0; i < strlen(ends); i++) {
+
+	len = strlen(ends);
+	for (i = 0; i < len; i++) {
 		if (toupper(buf[0]) == ends[i])
 			break;
 	}
-	if (i == strlen(ends)) {
+	if (i == len) {
 		if (hdl)
 			zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
 			    "invalid numeric suffix '%s'"), buf);
diff --git a/module/zcommon/zfs_prop.c b/module/zcommon/zfs_prop.c
index 8179a1a8c39d..f7e6b41bf012 100644
--- a/module/zcommon/zfs_prop.c
+++ b/module/zcommon/zfs_prop.c
@@ -808,11 +808,12 @@ zfs_name_to_prop(const char *propname)
 boolean_t
 zfs_prop_user(const char *name)
 {
-	int i;
+	int i, len;
 	char c;
 	boolean_t foundsep = B_FALSE;
 
-	for (i = 0; i < strlen(name); i++) {
+	len = strlen(name);
+	for (i = 0; i < len; i++) {
 		c = name[i];
 		if (!zprop_valid_char(c))
 			return (B_FALSE);
diff --git a/module/zcommon/zpool_prop.c b/module/zcommon/zpool_prop.c
index afdbb6f15e97..d3355730ba3d 100644
--- a/module/zcommon/zpool_prop.c
+++ b/module/zcommon/zpool_prop.c
@@ -494,11 +494,12 @@ vdev_name_to_prop(const char *propname)
 boolean_t
 vdev_prop_user(const char *name)
 {
-	int i;
+	int i, len;
 	char c;
 	boolean_t foundsep = B_FALSE;
 
-	for (i = 0; i < strlen(name); i++) {
+	len = strlen(name);
+	for (i = 0; i < len; i++) {
 		c = name[i];
 		if (!zprop_valid_char(c))
 			return (B_FALSE);
diff --git a/udev/zvol_id.c b/udev/zvol_id.c
index 609349594767..0d1da9956749 100644
--- a/udev/zvol_id.c
+++ b/udev/zvol_id.c
@@ -56,6 +56,7 @@ main(int argc, const char *const *argv)
 		return (1);
 	}
 	const char *dev_name = argv[1];
+	size_t i, len;
 
 	int fd;
 	struct stat sb;
@@ -73,11 +74,13 @@ main(int argc, const char *const *argv)
 	}
 
 	const char *dev_part = strrchr(dev_name, 'p');
+	len = strlen(zvol_name);
 	if (dev_part != NULL) {
-		sprintf(zvol_name + strlen(zvol_name), "-part%s", dev_part + 1);
+		sprintf(zvol_name + len, "-part%s", dev_part + 1);
+		len = strlen(zvol_name);
 	}
 
-	for (size_t i = 0; i < strlen(zvol_name); ++i)
+	for (i = 0; i < len; ++i)
 		if (isblank(zvol_name[i]))
 			zvol_name[i] = '+';