diff --git a/lang/el-compiler/runtime/el_runtime.c b/lang/el-compiler/runtime/el_runtime.c
index df25f4a..9320c1a 100644
--- a/lang/el-compiler/runtime/el_runtime.c
+++ b/lang/el-compiler/runtime/el_runtime.c
@@ -4999,7 +4999,13 @@ el_val_t state_get_or(el_val_t key, el_val_t default_val) {
 
 el_val_t float_to_str(el_val_t f) {
     char buf[64];
-    snprintf(buf, sizeof(buf), "%g", el_to_float(f));
+    double v = el_to_float(f);
+    /* Normalize NaN to "nan" regardless of sign — platform-independent. */
+    if (isnan(v)) {
+        snprintf(buf, sizeof(buf), "nan");
+    } else {
+        snprintf(buf, sizeof(buf), "%g", v);
+    }
     return el_wrap_str(el_strdup(buf));
 }