diff --git a/include/gsl/span b/include/gsl/span
index 737ef80..5049b97 100644
--- a/include/gsl/span
+++ b/include/gsl/span
@@ -143,14 +143,14 @@ namespace details
         constexpr reference operator*() const noexcept
         {
             Expects(begin_ && current_ && end_);
-            Expects(current_ < end_);
+            Expects(begin_ <= current_ && current_ < end_);
             return *current_;
         }
 
         constexpr pointer operator->() const noexcept
         {
             Expects(begin_ && current_ && end_);
-            Expects(current_ < end_);
+            Expects(begin_ <= current_ && current_ < end_);
             return current_;
         }
         constexpr span_iterator& operator++() noexcept
@@ -171,7 +171,7 @@ namespace details
         constexpr span_iterator& operator--() noexcept
         {
             Expects(begin_ && current_ && end_);
-            Expects(current_ > begin_);
+            Expects(begin_ < current_);
             --current_;
             return *this;
         }
@@ -295,7 +295,9 @@ namespace details
 
         constexpr void _Verify_offset(const difference_type n) const noexcept
         { // test that *this + n is within the range of this call
-            Expects( n <= (current_ - begin_)  && n <= (end_ - current_));
+            if (n != 0) Expects(begin_ && current_ && end_);
+            if (n > 0) Expects(end_ - current_ >= n);
+            if (n < 0) Expects(current_ - begin_ >= -n);
         }
 
         GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
index 8d9fadd..99ee0d8 100644
--- a/tests/span_tests.cpp
+++ b/tests/span_tests.cpp
@@ -105,17 +105,17 @@ TEST(span_test, from_nullptr_size_constructor)
         std::abort();
     });
     {
-        span<int> s{nullptr, narrow_cast<span<int>::index_type>(0)};
+        span<int> s{nullptr, narrow_cast<span<int>::size_type>(0)};
         EXPECT_TRUE(s.size() == 0);
         EXPECT_TRUE(s.data() == nullptr);
 
-        span<int> cs{nullptr, narrow_cast<span<int>::index_type>(0)};
+        span<int> cs{nullptr, narrow_cast<span<int>::size_type>(0)};
         EXPECT_TRUE(cs.size() == 0);
         EXPECT_TRUE(cs.data() == nullptr);
     }
     {
         auto workaround_macro = []() {
-            const span<int, 1> s{nullptr, narrow_cast<span<int>::index_type>(0)};
+            const span<int, 1> s{nullptr, narrow_cast<span<int>::size_type>(0)};
         };
         EXPECT_DEATH(workaround_macro(), deathstring);
     }
@@ -134,11 +134,11 @@ TEST(span_test, from_nullptr_size_constructor)
         EXPECT_DEATH(const_workaround_macro(), deathstring);
     }
     {
-        span<int*> s{nullptr, narrow_cast<span<int>::index_type>(0)};
+        span<int*> s{nullptr, narrow_cast<span<int>::size_type>(0)};
         EXPECT_TRUE(s.size() == 0);
         EXPECT_TRUE(s.data() == nullptr);
 
-        span<const int*> cs{nullptr, narrow_cast<span<int>::index_type>(0)};
+        span<const int*> cs{nullptr, narrow_cast<span<int>::size_type>(0)};
         EXPECT_TRUE(cs.size() == 0);
         EXPECT_TRUE(cs.data() == nullptr);
     }
@@ -193,7 +193,7 @@ TEST(span_test, from_pointer_length_constructor)
 
     {
         int* p = nullptr;
-        span<int> s{p, narrow_cast<span<int>::index_type>(0)};
+        span<int> s{p, narrow_cast<span<int>::size_type>(0)};
         EXPECT_TRUE(s.size() == 0);
         EXPECT_TRUE(s.data() == nullptr);
     }
@@ -214,7 +214,7 @@ TEST(span_test, from_pointer_length_constructor)
 
     {
         int* p = nullptr;
-        auto s = make_span(p, narrow_cast<span<int>::index_type>(0));
+        auto s = make_span(p, narrow_cast<span<int>::size_type>(0));
         EXPECT_TRUE(s.size() == 0);
         EXPECT_TRUE(s.data() == nullptr);
     }
diff --git a/tests/string_span_tests.cpp b/tests/string_span_tests.cpp
index dd5a0de..c1f8cf4 100644
--- a/tests/string_span_tests.cpp
+++ b/tests/string_span_tests.cpp
@@ -163,14 +163,14 @@ TEST(string_span_tests, TestConstructFromStdString)
 {
     std::string s = "Hello there world";
     cstring_span<> v = s;
-    EXPECT_TRUE(v.length() == static_cast<cstring_span<>::index_type>(s.length()));
+    EXPECT_TRUE(v.length() == static_cast<cstring_span<>::size_type>(s.length()));
 }
 
 TEST(string_span_tests, TestConstructFromStdVector)
 {
     std::vector<char> vec(5, 'h');
     string_span<> v{vec};
-    EXPECT_TRUE(v.length() == static_cast<string_span<>::index_type>(vec.size()));
+    EXPECT_TRUE(v.length() == static_cast<string_span<>::size_type>(vec.size()));
 }
 
 TEST(string_span_tests, TestStackArrayConstruction)
@@ -232,7 +232,7 @@ TEST(string_span_tests, TestToString)
     char stack_string[] = "Hello";
     cstring_span<> v = ensure_z(stack_string);
     auto s2 = gsl::to_string(v);
-    EXPECT_TRUE(static_cast<cstring_span<>::index_type>(s2.length()) == v.length());
+    EXPECT_TRUE(static_cast<cstring_span<>::size_type>(s2.length()) == v.length());
     EXPECT_TRUE(s2.length() == static_cast<size_t>(5));
 }
 
@@ -245,7 +245,7 @@ TEST(string_span_tests, TestToBasicString)
     char stack_string[] = "Hello";
     cstring_span<> v = ensure_z(stack_string);
     auto s2 = gsl::to_basic_string<char, std::char_traits<char>, ::std::allocator<char>>(v);
-    EXPECT_TRUE(static_cast<cstring_span<>::index_type>(s2.length()) == v.length());
+    EXPECT_TRUE(static_cast<cstring_span<>::size_type>(s2.length()) == v.length());
     EXPECT_TRUE(s2.length() == static_cast<size_t>(5));
 }