diff --git a/common/stringop.c b/common/stringop.c
index 4b8c9a384..f8b7aaec6 100644
--- a/common/stringop.c
+++ b/common/stringop.c
@@ -9,24 +9,17 @@
 #include "string.h"
 #include "list.h"
 
-const char whitespace[] = " \f\n\r\t\v";
+static const char whitespace[] = " \f\n\r\t\v";
 
-char *strip_whitespace(char *_str) {
-	if (*_str == '\0')
-		return _str;
-	char *strold = _str;
-	while (*_str == ' ' || *_str == '\t') {
-		_str++;
-	}
-	char *str = strdup(_str);
-	free(strold);
-	int i;
-	for (i = 0; str[i] != '\0'; ++i);
-	do {
-		i--;
-	} while (i >= 0 && (str[i] == ' ' || str[i] == '\t'));
-	str[i + 1] = '\0';
-	return str;
+void strip_whitespace(char *str) {
+	size_t len = strlen(str);
+	size_t start = strspn(str, whitespace);
+	memmove(str, &str[start], len + 1 - start);
+
+	if (!*str) return;
+
+	for (len -= start + 1; isspace(str[len]); --len) {}
+	str[len + 1] = '\0';
 }
 
 void strip_quotes(char *str) {
diff --git a/include/stringop.h b/include/stringop.h
index d1bfa29d0..f7ca60a51 100644
--- a/include/stringop.h
+++ b/include/stringop.h
@@ -3,10 +3,7 @@
 
 #include "list.h"
 
-// array of whitespace characters to use for delims
-extern const char whitespace[];
-
-char *strip_whitespace(char *str);
+void strip_whitespace(char *str);
 char *strip_comments(char *str);
 void strip_quotes(char *str);
 
diff --git a/sway/commands.c b/sway/commands.c
index 927434bcd..cd595b030 100644
--- a/sway/commands.c
+++ b/sway/commands.c
@@ -236,15 +236,15 @@ list_t *execute_command(char *_exec, struct sway_seat *seat,
 			criteria_destroy(criteria);
 			config->handler_context.using_criteria = true;
 			// Skip leading whitespace
-			head += strspn(head, whitespace);
+			for (; isspace(*head); ++head) {}
 		}
 		// Split command list
 		cmdlist = argsep(&head, ";");
-		cmdlist += strspn(cmdlist, whitespace);
+		for (; isspace(*cmdlist); ++cmdlist) {}
 		do {
 			// Split commands
 			cmd = argsep(&cmdlist, ",");
-			cmd += strspn(cmd, whitespace);
+			for (; isspace(*cmd); ++cmd) {}
 			if (strcmp(cmd, "") == 0) {
 				wlr_log(WLR_INFO, "Ignoring empty command.");
 				continue;
diff --git a/sway/config.c b/sway/config.c
index bb7f796d1..c71f315a2 100644
--- a/sway/config.c
+++ b/sway/config.c
@@ -580,7 +580,7 @@ static int detect_brace_on_following_line(FILE *file, char *line,
 			free(peeked);
 			peeked = peek_line(file, lines, &position);
 			if (peeked) {
-				peeked = strip_whitespace(peeked);
+				strip_whitespace(peeked);
 			}
 			lines++;
 		} while (peeked && strlen(peeked) == 0);
@@ -663,7 +663,7 @@ bool read_config(FILE *file, struct sway_config *config,
 			read += length + 1;
 		}
 
-		line = strip_whitespace(line);
+		strip_whitespace(line);
 		if (line[0] == '#') {
 			free(line);
 			continue;
diff --git a/sway/input/input-manager.c b/sway/input/input-manager.c
index 610877332..04e14355c 100644
--- a/sway/input/input-manager.c
+++ b/sway/input/input-manager.c
@@ -49,7 +49,7 @@ char *input_device_get_identifier(struct wlr_input_device *device) {
 	int vendor = device->vendor;
 	int product = device->product;
 	char *name = strdup(device->name);
-	name = strip_whitespace(name);
+	strip_whitespace(name);
 
 	char *p = name;
 	for (; *p; ++p) {