diff --git a/src/ops/builtins.c b/src/ops/builtins.c
index 74c48724..c2d4f82d 100644
--- a/src/ops/builtins.c
+++ b/src/ops/builtins.c
@@ -24,6 +24,7 @@
 /**   I/O builtins, type casting, and misc builtins extracted from eval.c.
  */
 
+#include <errno.h>
 #include "lang/eval.h"
 #include "lang/internal.h"
 #include "lang/env.h"
@@ -1342,8 +1343,13 @@ ray_t* ray_cast_fn(ray_t* type_sym, ray_t* val) {
             const char* sp = ray_str_ptr(val);
             if (!sp) return ray_error("domain", "as: cannot parse empty str as i64");
             char* end;
+            errno = 0;
             int64_t v = strtoll(sp, &end, 10);
             if (end == sp) return ray_error("domain", "as: cannot parse str as i64");
+            if (*end != '\0')
+                return ray_error("domain", "as: cannot parse str as i64, unexpected trailing characters");
+            if (errno == ERANGE)
+                return ray_error("domain", "as: cannot parse str as i64, value out of int64 range");
             return make_i64(v);
         }
         /* Vector/list cast */
@@ -1364,8 +1370,13 @@ ray_t* ray_cast_fn(ray_t* type_sym, ray_t* val) {
         if (val->type == -RAY_TIMESTAMP) return ray_i32((int32_t)val->i64);
         if (val->type == -RAY_STR) {
             const char* sp = ray_str_ptr(val); char* end;
+            errno = 0;
             long v = strtol(sp, &end, 10);
             if (end == sp) return ray_error("domain", "as: cannot parse str as i32");
+            if (*end != '\0')
+                return ray_error("domain", "as: cannot parse str as i32, unexpected trailing characters");
+            if (errno == ERANGE)
+                return ray_error("domain", "as: cannot parse str as i32, value out of int64 range");
             return ray_i32((int32_t)v);
         }
         /* Vector cast */
@@ -1386,8 +1397,13 @@ ray_t* ray_cast_fn(ray_t* type_sym, ray_t* val) {
         if (val->type == -RAY_TIMESTAMP) return ray_i16((int16_t)val->i64);
         if (val->type == -RAY_STR) {
             const char* sp = ray_str_ptr(val); char* end;
+            errno = 0;
             long v = strtol(sp, &end, 10);
             if (end == sp) return ray_error("domain", "as: cannot parse str as i16");
+            if (*end != '\0')
+                return ray_error("domain", "as: cannot parse str as i16, unexpected trailing characters");
+            if (errno == ERANGE)
+                return ray_error("domain", "as: cannot parse str as i16, value out of int64 range");
             return ray_i16((int16_t)v);
         }
         /* Vector cast */
@@ -1410,8 +1426,11 @@ ray_t* ray_cast_fn(ray_t* type_sym, ray_t* val) {
             const char* sp = ray_str_ptr(val);
             if (!sp) return ray_error("domain", "as: cannot parse empty str as f64");
             char* end;
+            errno = 0;
             double v = strtod(sp, &end);
             if (end == sp) return ray_error("domain", "as: cannot parse str as f64");
+            if (*end != '\0')
+                return ray_error("domain", "as: cannot parse str as f64, unexpected trailing characters");
             /* STAGE 2 (ingest/cast STR→F64): canonicalize at the ingest entry
              * point.  strtod("inf")/strtod("1e400")/strtod("nan") would yield a
              * non-finite F64; make_f64 maps every non-finite to NULL_F64 (0Nf),
@@ -1900,8 +1919,13 @@ ray_t* ray_cast_fn(ray_t* type_sym, ray_t* val) {
         if (val->type == -RAY_F64) return ray_u8(ray_cast_f64_to_u8_null(val->f64));
         if (val->type == -RAY_STR) {
             const char* sp = ray_str_ptr(val);
-            char* end; long v = strtol(sp, &end, 10);
+            char* end; errno = 0;
+            long v = strtol(sp, &end, 10);
             if (end == sp) return ray_error("domain", "as: cannot parse str as u8");
+            if (*end != '\0')
+                return ray_error("domain", "as: cannot parse str as u8, unexpected trailing characters");
+            if (errno == ERANGE)
+                return ray_error("domain", "as: cannot parse str as u8, value out of int64 range");
             return ray_u8((uint8_t)v);
         }
         /* Vector cast */
diff --git a/test/rfl/type/as.rfl b/test/rfl/type/as.rfl
index 7bc4825c..15c98ad1 100644
--- a/test/rfl/type/as.rfl
+++ b/test/rfl/type/as.rfl
@@ -527,6 +527,36 @@
 (as 'i64 (as 'i32 "-2147483648")) -- 0Nl
 (as 'i64 (as 'i32 "2147483647")) -- 2147483647
 
+;; ========== STRING → NUMERIC: FULL CONSUMPTION + OVERFLOW ==========
+;; The old strtoll/strtol/strtod path stopped at the first non-digit and
+;; never checked the end pointer or ERANGE, so trailing garbage and true
+;; overflow were silently accepted ("1e19" → 1, "9999...9" → INT64_MAX).
+;; All of these must now REJECT with a domain error, matching the strict
+;; DATE/TIME/TIMESTAMP string casts.  Narrow-int truncation itself still
+;; wraps (documented narrow-int rule); only unparseable/overflowing input
+;; errors.
+(as 'i64 "123abc") !- domain
+(as 'i64 "1e19") !- domain
+(as 'i64 "12.5") !- domain
+(as 'i64 "999999999999999999999999") !- domain
+(as 'i64 "-999999999999999999999999") !- domain
+(as 'i32 "123x") !- domain
+(as 'i32 "1e9") !- domain
+(as 'i16 "40000junk") !- domain
+(as 'u8 "12zz") !- domain
+(as 'u8 "300abc") !- domain
+(as 'f64 "1.5x") !- domain
+(as 'f64 "1.5e3junk") !- domain
+;; Clean values still parse.
+(as 'i64 " 123") -- 123
+(as 'i64 "-5") -- -5
+(as 'f64 "0x10") -- 16.0
+;; The string-VECTOR cast routes through the same per-element parser: a
+;; malformed element rejects the whole cast, clean elements parse.
+(as 'I64 (list "42" "-7" "100")) -- [42 -7 100]
+(as 'I64 (list "42" "123abc")) !- domain
+(as 'F64 (list "3.14" "1.5x")) !- domain
+
 ;; ========== NULL PRESERVATION ACROSS CASTS ==========
 ;; Casting any null returns null of target type, never sentinel/INT_MIN.
 (nil? (as 'i64 0Nh)) -- true