diff --git a/src/libguac/string.c b/src/libguac/string.c
index c913b4a4..f05c4c06 100644
--- a/src/libguac/string.c
+++ b/src/libguac/string.c
@@ -22,6 +22,26 @@
 #include <stddef.h>
 #include <string.h>
 
+/**
+ * Returns the space remaining in a buffer assuming that the given number of
+ * bytes have already been written. If the number of bytes exceeds the size
+ * of the buffer, zero is returned.
+ *
+ * @param n
+ *     The size of the buffer in bytes.
+ *
+ * @param length
+ *     The number of bytes which have been written to the buffer so far. If
+ *     the routine writing the bytes will automatically truncate its writes,
+ *     this value may exceed the size of the buffer.
+ *
+ * @return
+ *     The number of bytes remaining in the buffer. This value will always
+ *     be non-negative. If the number of bytes written already exceeds the
+ *     size of the buffer, zero will be returned.
+ */
+#define REMAINING(n, length) (((n) < (length)) ? 0 : ((n) - (length)))
+
 size_t guac_strlcpy(char* restrict dest, const char* restrict src, size_t n) {
 
 #ifdef HAVE_STRLCPY
@@ -31,7 +51,7 @@ size_t guac_strlcpy(char* restrict dest, const char* restrict src, size_t n) {
     size_t length = strlen(src);
 
     /* Copy nothing if there is no space */
-    if (n <= 0)
+    if (n == 0)
         return length;
 
     /* Calculate length of the string which will be copied */
@@ -55,8 +75,8 @@ size_t guac_strlcat(char* restrict dest, const char* restrict src, size_t n) {
 #ifdef HAVE_STRLCPY
     return strlcat(dest, src, n);
 #else
-    int length = strnlen(dest, n);
-    return length + guac_strlcpy(dest + length, src, n - length);
+    size_t length = strnlen(dest, n);
+    return length + guac_strlcpy(dest + length, src, REMAINING(n, length));
 #endif
 
 }
@@ -64,7 +84,7 @@ size_t guac_strlcat(char* restrict dest, const char* restrict src, size_t n) {
 size_t guac_strljoin(char* restrict dest, const char* restrict const* elements,
         int nmemb, const char* restrict delim, size_t n) {
 
-    int length = 0;
+    size_t length = 0;
     const char* restrict const* current = elements;
 
     /* If no elements are provided, nothing to do but ensure the destination
@@ -77,8 +97,8 @@ size_t guac_strljoin(char* restrict dest, const char* restrict const* elements,
 
     /* Copy all remaining elements, separated by delimiter */
     for (current++; nmemb > 1; current++, nmemb--) {
-        length += guac_strlcat(dest + length, delim, n - length);
-        length += guac_strlcat(dest + length, *current, n - length);
+        length += guac_strlcat(dest + length, delim, REMAINING(n, length));
+        length += guac_strlcat(dest + length, *current, REMAINING(n, length));
     }
 
     return length;