diff --git a/include/gsl/gsl_algorithm b/include/gsl/gsl_algorithm
index c2ba31f..6813b6c 100644
--- a/include/gsl/gsl_algorithm
+++ b/include/gsl/gsl_algorithm
@@ -37,8 +37,8 @@ namespace gsl
 {
 // Note: this will generate faster code than std::copy using span iterator in older msvc+stl
 // not necessary for msvc since VS2017 15.8 (_MSC_VER >= 1915)
-template <class SrcElementType, std::ptrdiff_t SrcExtent, class DestElementType,
-          std::ptrdiff_t DestExtent>
+template <class SrcElementType, std::size_t SrcExtent, class DestElementType,
+          std::size_t DestExtent>
 void copy(span<SrcElementType, SrcExtent> src, span<DestElementType, DestExtent> dest)
 {
     static_assert(std::is_assignable<decltype(*dest.data()), decltype(*src.data())>::value,
diff --git a/include/gsl/span b/include/gsl/span
index 1b06fb3..6e7e791 100644
--- a/include/gsl/span
+++ b/include/gsl/span
@@ -592,7 +592,7 @@ private:
         }
         else
         {
-            return idx >= 0 && idx < size;
+            return idx < size;
         }
     }
 
diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
index d94ed20..ac05af1 100644
--- a/tests/span_tests.cpp
+++ b/tests/span_tests.cpp
@@ -966,7 +966,7 @@ TEST(span_test, from_array_constructor)
          EXPECT_TRUE(av.subspan(5).size() == 0);
          EXPECT_DEATH(av.subspan(6).size(), deathstring);
          const auto av2 = av.subspan(1);
-         for (std::size_t i = 0; i < 4; ++i) EXPECT_TRUE(av2[i] == i + 2);
+         for (std::size_t i = 0; i < 4; ++i) EXPECT_TRUE(av2[i] == static_cast<int>(i) + 2);
      }
 
      {
@@ -977,7 +977,7 @@ TEST(span_test, from_array_constructor)
          EXPECT_TRUE(av.subspan(5).size() == 0);
          EXPECT_DEATH(av.subspan(6).size(), deathstring);
          const auto av2 = av.subspan(1);
-         for (std::size_t i = 0; i < 4; ++i) EXPECT_TRUE(av2[i] == i + 2);
+         for (std::size_t i = 0; i < 4; ++i) EXPECT_TRUE(av2[i] == static_cast<int>(i) + 2);
      }
  }
 
diff --git a/tests/string_span_tests.cpp b/tests/string_span_tests.cpp
index e501bba..dd5a0de 100644
--- a/tests/string_span_tests.cpp
+++ b/tests/string_span_tests.cpp
@@ -84,7 +84,7 @@ czstring_span<> CreateTempName(string_span<> span)
 {
     Expects(span.size() > 1);
 
-    int last = 0;
+    std::size_t last = 0;
     if (span.size() > 4) {
         span[0] = 't';
         span[1] = 'm';
@@ -101,7 +101,7 @@ cwzstring_span<> CreateTempNameW(wstring_span<> span)
 {
     Expects(span.size() > 1);
 
-    int last = 0;
+    std::size_t last = 0;
     if (span.size() > 4) {
         span[0] = L't';
         span[1] = L'm';
@@ -118,7 +118,7 @@ cu16zstring_span<> CreateTempNameU16(u16string_span<> span)
 {
     Expects(span.size() > 1);
 
-    int last = 0;
+    std::size_t last = 0;
     if (span.size() > 4) {
         span[0] = u't';
         span[1] = u'm';
@@ -135,7 +135,7 @@ cu32zstring_span<> CreateTempNameU32(u32string_span<> span)
 {
     Expects(span.size() > 1);
 
-    int last = 0;
+    std::size_t last = 0;
     if (span.size() > 4) {
         span[0] = U't';
         span[1] = U'm';