diff --git a/XUtils.c b/XUtils.c
index 743d98bf..cd5edb91 100644
--- a/XUtils.c
+++ b/XUtils.c
@@ -184,13 +184,13 @@ int xAsprintf(char** strp, const char* fmt, ...) {
    return r;
 }
 
-int xSnprintf(char* buf, int len, const char* fmt, ...) {
+int xSnprintf(char* buf, size_t len, const char* fmt, ...) {
    va_list vl;
    va_start(vl, fmt);
    int n = vsnprintf(buf, len, fmt, vl);
    va_end(vl);
 
-   if (n < 0 || n >= len) {
+   if (n < 0 || (size_t)n >= len) {
       fail();
    }
 
diff --git a/XUtils.h b/XUtils.h
index e0aeebe2..19cfadb3 100644
--- a/XUtils.h
+++ b/XUtils.h
@@ -59,7 +59,7 @@ ATTR_FORMAT(printf, 2, 3)
 int xAsprintf(char** strp, const char* fmt, ...);
 
 ATTR_FORMAT(printf, 3, 4)
-int xSnprintf(char* buf, int len, const char* fmt, ...);
+int xSnprintf(char* buf, size_t len, const char* fmt, ...);
 
 char* xStrdup(const char* str) ATTR_NONNULL;