diff --git a/headers/posix/string.h b/headers/posix/string.h
index 0a866812be..802abcd522 100644
--- a/headers/posix/string.h
+++ b/headers/posix/string.h
@@ -77,6 +77,8 @@ extern const char	*strsignal(int signal);
 #define bcopy(source, dest, length) memcpy((dest), (source), (length))
 #define bzero(buffer, length) memset((buffer), 0, (length))
 
+extern int ffs(int i);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/kernel/libroot/posix/string/ffs.cpp b/src/kernel/libroot/posix/string/ffs.cpp
new file mode 100644
index 0000000000..7f5ff3f6b3
--- /dev/null
+++ b/src/kernel/libroot/posix/string/ffs.cpp
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2005, Ingo Weinhold, bonefish@users.sf.net.
+ * Distributed under the terms of the MIT License.
+ */
+
+#include <strings.h>
+
+// find first (least significant) set bit
+int
+ffs(int value)
+{
+	if (!value)
+		return 0;
+
+	// ToDo: This can certainly be optimized (e.g. by binary search). Or not
+	// unlikely there's a single assembler instruction...
+	for (int i = 1; i <= (int)sizeof(value) * 8; i++, value >>= 1) {
+		if (value & 1)
+			return i;
+	}
+
+	// never gets here
+	return 0;
+}