diff --git a/src/header/stdlib/mod.rs b/src/header/stdlib/mod.rs
index 3a4dbb1cb7..cef9cdcdd1 100644
--- a/src/header/stdlib/mod.rs
+++ b/src/header/stdlib/mod.rs
@@ -454,35 +454,51 @@ pub unsafe extern "C" fn getenv(name: *const c_char) -> *mut c_char {
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn getsubopt(
     optionp: *mut *mut c_char,
-    tokens: *const *mut c_char,
+    keylistp: *const *mut c_char,
     valuep: *mut *mut c_char,
 ) -> c_int {
+    if optionp.is_null() || (*optionp).is_null() || keylistp.is_null() || valuep.is_null() {
+        return -1;
+    }
+
     let start = *optionp;
-    let max = strlen(start) as isize;
-    let mut i: usize = 0;
-    *valuep = ptr::null_mut();
-    *optionp = strchr(start, b',' as i32);
-    if !(*optionp).is_null() {
-        *(*optionp).add(0) = 0;
-        *optionp = *optionp.add(1);
-    } else {
-        *(optionp) = start.add(max as usize);
-    }
-    while !tokens.offset(i as isize).is_null() {
-        let cur = tokens.offset(i as isize) as *const _;
-        let len = strlen(cur) as isize;
-        if strncmp(cur, start, len as usize) != 0 {
-            i = i + 1;
-            continue;
+    let mut cursor = start;
+    let mut found_comma = false;
+
+    while *cursor != 0 {
+        if *cursor == b',' as c_char {
+            *cursor = 0;
+            *optionp = cursor.add(1);
+            found_comma = true;
+            break;
         }
-        if (*start.offset(len)) == b'=' as c_char {
-            *valuep = start.offset(len + 1);
-        } else if !start.offset(len).is_null() {
-            i = i + 1;
-            continue;
-        }
-        return i as c_int;
+        cursor = cursor.add(1);
     }
+
+    if !found_comma {
+        *optionp = cursor;
+    }
+
+    let mut i = 0;
+    while !(*keylistp.add(i)).is_null() {
+        let token = *keylistp.add(i);
+        let token_len = strlen(token);
+
+        if strncmp(start, token, token_len) == 0 {
+            let suffix_char = *start.add(token_len);
+
+            if suffix_char == b'=' as c_char {
+                *valuep = start.add(token_len + 1);
+                return i as c_int;
+            } else if suffix_char == 0 {
+                *valuep = ptr::null_mut();
+                return i as c_int;
+            }
+        }
+        i += 1;
+    }
+
+    *valuep = start;
     -1
 }
 
diff --git a/tests/Makefile b/tests/Makefile
index 4e6e3e7e73..08ccf04764 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -80,6 +80,7 @@ EXPECT_NAMES=\
 	stdlib/atoi \
 	stdlib/div \
 	stdlib/env \
+	stdlib/getsubopt \
 	stdlib/mkostemps \
 	stdlib/qsort \
 	stdlib/rand \
diff --git a/tests/expected/bins_static/stdlib/getsubopt.stderr b/tests/expected/bins_static/stdlib/getsubopt.stderr
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/expected/bins_static/stdlib/getsubopt.stdout b/tests/expected/bins_static/stdlib/getsubopt.stdout
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/stdlib/getsubopt.c b/tests/stdlib/getsubopt.c
new file mode 100644
index 0000000000..4717f65fcd
--- /dev/null
+++ b/tests/stdlib/getsubopt.c
@@ -0,0 +1,55 @@
+#include "test_helpers.h"
+
+int main(void) {
+    char *const tokens[] = {
+        "ro",
+        "rw",
+        "foo",
+        "baz",
+        NULL
+    };
+
+    // getsubopt modifies the string in-place
+    char opt_str[] = "ro,foo=bar,bool,baz=,rw";
+    char *options = opt_str;
+    char *value = NULL;
+    int idx;
+
+    idx = getsubopt(&options, tokens, &value);
+    UNEXP_IF(getsubopt, idx, != 0);
+    if (value != NULL) {
+        printf("getsubopt failed: expected NULL value for 'ro', got '%s'\n", value);
+        exit(EXIT_FAILURE);
+    }
+
+    idx = getsubopt(&options, tokens, &value);
+    UNEXP_IF(getsubopt, idx, != 2);
+    if (value == NULL || strcmp(value, "bar") != 0) {
+        printf("getsubopt failed: expected 'bar', got '%s'\n", value ? value : "NULL");
+        exit(EXIT_FAILURE);
+    }
+
+    idx = getsubopt(&options, tokens, &value);
+    UNEXP_IF(getsubopt, idx, != -1);
+    if (value == NULL || strcmp(value, "bool") != 0) {
+        printf("getsubopt failed: expected 'bool' in value, got '%s'\n", value ? value : "NULL");
+        exit(EXIT_FAILURE);
+    }
+
+    idx = getsubopt(&options, tokens, &value);
+    UNEXP_IF(getsubopt, idx, != 3);
+    if (value == NULL || strcmp(value, "") != 0) {
+        printf("getsubopt failed: expected empty string value, got '%s'\n", value ? value : "NULL");
+        exit(EXIT_FAILURE);
+    }
+
+    idx = getsubopt(&options, tokens, &value);
+    UNEXP_IF(getsubopt, idx, != 1);
+    if (value != NULL) {
+        printf("getsubopt failed: expected NULL value for 'rw', got '%s'\n", value);
+        exit(EXIT_FAILURE);
+    }
+
+    idx = getsubopt(&options, tokens, &value);
+    UNEXP_IF(getsubopt, idx, != -1);
+}