diff --git a/include/xlnt/utils/optional.hpp b/include/xlnt/utils/optional.hpp
index 934a9aea..2201b68b 100644
--- a/include/xlnt/utils/optional.hpp
+++ b/include/xlnt/utils/optional.hpp
@@ -38,7 +38,8 @@ namespace xlnt {
 template <typename T>
 class optional
 {
-#if defined(_MSC_VER) && _MSC_VER <= 1900 // v14, visual studio 2015
+#if ((defined(_MSC_VER) && _MSC_VER <= 1900) || (defined(__GNUC__) && __GNUC__ < 5))
+// Disable enhanced type checking on Visual Studio <= 2015 and GCC <5
 #define XLNT_NOEXCEPT_VALUE_COMPAT(...) (false)
 #else
 #define XLNT_NOEXCEPT_VALUE_COMPAT(...) (__VA_ARGS__)
diff --git a/source/detail/cryptography/sha1.c b/source/detail/cryptography/sha1.c
index f5412dc8..00a67818 100644
--- a/source/detail/cryptography/sha1.c
+++ b/source/detail/cryptography/sha1.c
@@ -174,7 +174,8 @@ void sha1_hash(const uint8_t *message, size_t len, uint32_t hash[5]) {
 
     block[BLOCK_SIZE - 1] = (uint8_t)((len & 0x1FU) << 3);
     len >>= 5;
-    for (int i = 1; i < LENGTH_SIZE; i++, len >>= 8)
+	int i;
+    for (i = 1; i < LENGTH_SIZE; i++, len >>= 8)
         block[BLOCK_SIZE - 1 - i] = (uint8_t)(len & 0xFFU);
     sha1_compress(hash, block);
 }
diff --git a/source/detail/cryptography/sha512.c b/source/detail/cryptography/sha512.c
index 0d59e2c8..d5328684 100644
--- a/source/detail/cryptography/sha512.c
+++ b/source/detail/cryptography/sha512.c
@@ -261,7 +261,8 @@ void sha512_hash(const uint8_t *message, size_t len, uint64_t hash[8]) {
 
     block[BLOCK_SIZE - 1] = (uint8_t)((len & 0x1FU) << 3);
     len >>= 5;
-    for (int i = 1; i < LENGTH_SIZE; i++, len >>= 8)
+	int i;
+    for (i = 1; i < LENGTH_SIZE; i++, len >>= 8)
         block[BLOCK_SIZE - 1 - i] = (uint8_t)(len & 0xFFU);
     sha512_compress(hash, block);
 }
diff --git a/source/detail/serialization/custom_value_traits.hpp b/source/detail/serialization/custom_value_traits.hpp
index f013815c..ba477f29 100644
--- a/source/detail/serialization/custom_value_traits.hpp
+++ b/source/detail/serialization/custom_value_traits.hpp
@@ -199,8 +199,8 @@ pattern_fill_type from_string(const std::string &string)
 #pragma clang diagnostic pop
     
     auto toLower = [](std::string str) {
-        auto bg{ std::begin (str) };
-        auto en{ std::end (str) };
+        auto bg = std::begin (str);
+        auto en = std::end (str);
         std::transform(bg, en, bg, 
                        [](char c) {
                         // static cast to avoid int -> char narrowing warning
@@ -211,7 +211,7 @@ pattern_fill_type from_string(const std::string &string)
     };
 
     auto patternLookup = [](const std::string& key) {
-        auto entry { patternFill.find (key) };
+        auto entry = patternFill.find (key);
         if (entry != std::end (patternFill)) {
             return entry->second;
         }