diff --git a/src/lib/utils/int_utils.h b/src/lib/utils/int_utils.h
index 2c943f4d402..76e42a88190 100644
--- a/src/lib/utils/int_utils.h
+++ b/src/lib/utils/int_utils.h
@@ -17,7 +17,7 @@ namespace Botan {
 template <std::unsigned_integral T>
 constexpr inline std::optional<T> checked_add(T a, T b) {
    const T r = a + b;
-   if(r - a != b) {
+   if(r < a || r < b) {
       return {};
    }
    return r;
diff --git a/src/tests/test_utils.cpp b/src/tests/test_utils.cpp
index d3917852fec..e82c384d12a 100644
--- a/src/tests/test_utils.cpp
+++ b/src/tests/test_utils.cpp
@@ -14,6 +14,7 @@
 #include <botan/internal/cpuid.h>
 #include <botan/internal/ct_utils.h>
 #include <botan/internal/fmt.h>
+#include <botan/internal/int_utils.h>
 #include <botan/internal/loadstor.h>
 #include <botan/internal/parsing.h>
 #include <botan/internal/rounding.h>
@@ -38,6 +39,9 @@ class Utility_Function_Tests final : public Test {
       std::vector<Test::Result> run() override {
          std::vector<Test::Result> results;
 
+         results.push_back(test_checked_add());
+         results.push_back(test_checked_mul());
+         results.push_back(test_checked_cast());
          results.push_back(test_round_up());
          results.push_back(test_loadstore());
          results.push_back(test_loadstore_fallback());
@@ -47,6 +51,82 @@ class Utility_Function_Tests final : public Test {
       }
 
    private:
+      Test::Result test_checked_add() {
+         Test::Result result("checked_add");
+
+         const size_t large = static_cast<size_t>(-5);
+         const size_t zero = 0;
+
+         for(int si = -15; si != 15; ++si) {
+            const size_t i = static_cast<size_t>(si);
+            auto sum1 = Botan::checked_add<size_t>(i, zero, zero, zero, large);
+            auto sum2 = Botan::checked_add<size_t>(large, zero, zero, zero, i);
+
+            result.confirm("checked_add looks at all args", sum1 == sum2);
+
+            if(i < 5) {
+               result.test_eq("checked_add worked", sum1.value(), i + large);
+            } else {
+               result.confirm("checked_add did not return a result", !sum1.has_value());
+            }
+         }
+
+         auto& rng = Test::rng();
+
+         for(size_t i = 0; i != 100; ++i) {
+            const uint16_t x = Botan::make_uint16(rng.next_byte(), rng.next_byte());
+            const uint16_t y = Botan::make_uint16(rng.next_byte(), rng.next_byte());
+
+            const uint32_t ref = static_cast<uint32_t>(x) + y;
+
+            if(auto z = Botan::checked_add(x, y)) {
+               result.test_int_eq("checked_add adds", z.value(), ref);
+            } else {
+               result.confirm("checked_add checks", (ref >> 16) > 0);
+            }
+         }
+
+         return result;
+      }
+
+      Test::Result test_checked_mul() {
+         Test::Result result("checked_mul");
+
+         auto& rng = Test::rng();
+
+         for(size_t i = 0; i != 100; ++i) {
+            const uint16_t x = Botan::make_uint16(rng.next_byte(), rng.next_byte());
+            const uint16_t y = Botan::make_uint16(rng.next_byte(), rng.next_byte());
+
+            const uint32_t ref = static_cast<uint32_t>(x) * y;
+
+            if(auto z = Botan::checked_mul(x, y)) {
+               result.test_int_eq("checked_mul multiplies", z.value(), ref);
+            } else {
+               result.confirm("checked_mul checks", (ref >> 16) > 0);
+            }
+         }
+
+         return result;
+      }
+
+      Test::Result test_checked_cast() {
+         Test::Result result("checked_cast");
+
+         const uint32_t large = static_cast<uint32_t>(-1);
+         const uint32_t is_16_bits = 0x8123;
+         const uint32_t is_8_bits = 0x89;
+
+         result.confirm("checked_cast checks", !Botan::checked_cast<uint16_t>(large).has_value());
+         result.confirm("checked_cast checks", !Botan::checked_cast<uint8_t>(large).has_value());
+
+         result.test_int_eq("checked_cast converts", Botan::checked_cast<uint32_t>(large).value(), large);
+         result.test_int_eq("checked_cast converts", Botan::checked_cast<uint16_t>(is_16_bits).value(), 0x8123);
+         result.test_int_eq("checked_cast converts", Botan::checked_cast<uint8_t>(is_8_bits).value(), 0x89);
+
+         return result;
+      }
+
       Test::Result test_round_up() {
          Test::Result result("Util round_up");