diff --git a/args.hxx b/args.hxx
index 86a8672..39c6f17 100644
--- a/args.hxx
+++ b/args.hxx
@@ -3761,6 +3761,14 @@ namespace args
             }
 
             const char *begin = value.c_str();
+            // The true end of the value, derived from its length rather than
+            // from the first NUL. strtoull/strtoll treat the buffer as a C
+            // string and stop at an embedded '\0', so checking `*end == '\0'`
+            // for "no trailing data" is defeated by a value like "12\0junk":
+            // end lands on the embedded NUL and the junk after it is silently
+            // accepted. Comparing against `stop` validates the whole string
+            // and matches the istringstream-based reader used for other types.
+            const char *const stop = begin + value.size();
 
             // C++11-compatible: use strtoull/strtoll. Hardening retained from
             // the original from_chars draft (errno save/restore, ERANGE check,
@@ -3779,11 +3787,11 @@ namespace args
                     errno = saved_errno;
                     return false;
                 }
-                while (*end != '\0' && std::isspace(static_cast<unsigned char>(*end)))
+                while (end != stop && std::isspace(static_cast<unsigned char>(*end)))
                 {
                     ++end;
                 }
-                if (*end != '\0' || errno == ERANGE ||
+                if (end != stop || errno == ERANGE ||
                     parsed > static_cast<unsigned long long>(std::numeric_limits<T>::max()))
                 {
                     errno = saved_errno;
@@ -3800,11 +3808,11 @@ namespace args
                     errno = saved_errno;
                     return false;
                 }
-                while (*end != '\0' && std::isspace(static_cast<unsigned char>(*end)))
+                while (end != stop && std::isspace(static_cast<unsigned char>(*end)))
                 {
                     ++end;
                 }
-                if (*end != '\0' || errno == ERANGE ||
+                if (end != stop || errno == ERANGE ||
                     parsed < static_cast<long long>(std::numeric_limits<T>::min()) ||
                     parsed > static_cast<long long>(std::numeric_limits<T>::max()))
                 {
diff --git a/test/embedded_nul_numeric.cxx b/test/embedded_nul_numeric.cxx
new file mode 100644
index 0000000..c4bfd5f
--- /dev/null
+++ b/test/embedded_nul_numeric.cxx
@@ -0,0 +1,82 @@
+// Regression test: the integer reader must not silently accept data that
+// follows an embedded NUL byte in the value string.
+//
+// ValueReader::ParseNumericValue for integer types parses value.c_str() with
+// std::strtoull/strtoll, which treat the buffer as a C string and stop at the
+// first '\0'. The "no trailing data" guard used to test `*end == '\0'`, which
+// an embedded NUL satisfies prematurely: "12\0garbage" was accepted as 12 and
+// everything past the NUL was silently discarded (an input-validation bypass,
+// CWE-158). The istringstream-based reader used for floating point already
+// rejected such input, so the two paths disagreed. The guard now validates
+// against the string's true length, so both paths reject trailing data
+// regardless of embedded NULs.
+//
+// This test FAILS on the unfixed library (the integer cases parse as success)
+// and passes once the length-based check is in place.
+
+#include "test_common.hxx"
+#include <args.hxx>
+#include "test_helpers.hxx"
+#include <iostream>
+#include <string>
+
+template <typename T>
+static void expect_reject(const std::string &input)
+{
+    args::ValueReader reader;
+    T val = 0;
+    const bool success = reader.ParseNumericValue(input, val);
+    if (success)
+    {
+        std::cerr << "FAIL: value with embedded NUL (size " << input.size()
+                  << ") was accepted as " << static_cast<long long>(val)
+                  << " but should have been rejected" << std::endl;
+        exit(1);
+    }
+}
+
+template <typename T>
+static void expect_accept(const std::string &input, T expected)
+{
+    args::ValueReader reader;
+    T val = 0;
+    const bool success = reader.ParseNumericValue(input, val);
+    if (!success)
+    {
+        std::cerr << "FAIL: valid value '" << input << "' was rejected" << std::endl;
+        exit(1);
+    }
+    if (val != expected)
+    {
+        std::cerr << "FAIL: value '" << input << "' parsed as "
+                  << static_cast<long long>(val) << " (expected "
+                  << static_cast<long long>(expected) << ")" << std::endl;
+        exit(1);
+    }
+}
+
+int main()
+{
+    const std::string nul(1, '\0');
+
+    // Data after an embedded NUL must not be silently dropped.
+    expect_reject<int>("12" + nul + "garbage");
+    expect_reject<long long>("34" + nul + "99");
+    expect_reject<unsigned int>("12" + nul + "garbage");
+    expect_reject<unsigned long long>("7" + nul + nul);
+    // Trailing whitespace followed by an embedded NUL and junk: the
+    // whitespace-tolerance loop must still stop at the true end.
+    expect_reject<int>("12 " + nul + "x");
+    // A NUL on its own is not a number.
+    expect_reject<int>(nul);
+
+    // Genuinely valid values, including the whitespace tolerance and the
+    // base-0 hex/octal forms, must keep parsing.
+    expect_accept<int>("12", 12);
+    expect_accept<int>("  -7  ", -7);
+    expect_accept<int>("0x10", 16);
+    expect_accept<unsigned int>("010", 8);
+
+    std::cout << "embedded NUL numeric tests passed!" << std::endl;
+    return 0;
+}