diff --git a/lib/core/include/irods/authentication_plugin_framework.hpp b/lib/core/include/irods/authentication_plugin_framework.hpp
index 60f05cf651..7d2365a2fc 100644
--- a/lib/core/include/irods/authentication_plugin_framework.hpp
+++ b/lib/core/include/irods/authentication_plugin_framework.hpp
@@ -16,6 +16,7 @@
 #include <fmt/format.h>
 #include <nlohmann/json.hpp>
 
+#include <cctype>
 #include <functional>
 #include <memory>
 #include <string>
@@ -117,7 +118,7 @@ namespace irods::experimental::auth
         using plugin_type = authentication_base;
 
         std::string scheme = _scheme;
-        std::transform(scheme.begin(), scheme.end(), scheme.begin(), ::tolower);
+        std::transform(scheme.begin(), scheme.end(), scheme.begin(), [](unsigned char _ch) { return std::tolower(_ch); });
 
         const std::string name = fmt::format("irods_auth_plugin-{}_{}", scheme, _type);
 
diff --git a/lib/core/include/irods/experimental_plugin_framework.hpp b/lib/core/include/irods/experimental_plugin_framework.hpp
index 8a80a2aacf..90c83dee03 100644
--- a/lib/core/include/irods/experimental_plugin_framework.hpp
+++ b/lib/core/include/irods/experimental_plugin_framework.hpp
@@ -15,6 +15,7 @@
 
 // =-=-=-=-=-=-=-
 // stl includes
+#include <cctype>
 #include <sstream>
 #include <string>
 #include <iostream>
@@ -148,7 +149,7 @@ namespace irods::experimental::api {
             std::transform(lower.begin(),
                            lower.end(),
                            lower.begin(),
-                           ::tolower );
+                           [](unsigned char _ch) { return std::tolower(_ch); });
 
             base* plugin{};
             auto err = irods::load_plugin<base>(
diff --git a/lib/core/include/irods/irods_query.hpp b/lib/core/include/irods/irods_query.hpp
index 9d9bf60a57..ff460c4a40 100644
--- a/lib/core/include/irods/irods_query.hpp
+++ b/lib/core/include/irods/irods_query.hpp
@@ -16,6 +16,7 @@
 #include <fmt/format.h>
 
 #include <algorithm>
+#include <cctype>
 #include <string>
 #include <vector>
 
@@ -48,7 +49,7 @@ namespace irods
                 lowered.begin(),
                 lowered.end(),
                 lowered.begin(),
-                ::tolower);
+                [](unsigned char _ch) { return std::tolower(_ch); });
 
             if(GEN_STR == lowered) {
                 return GENERAL;
diff --git a/lib/core/src/clientLogin.cpp b/lib/core/src/clientLogin.cpp
index ad83a2930a..9312915469 100644
--- a/lib/core/src/clientLogin.cpp
+++ b/lib/core/src/clientLogin.cpp
@@ -25,6 +25,7 @@
 
 #include <fmt/format.h>
 
+#include <cctype>
 #include <cerrno>
 #include <cstdint>
 #include <cstring>
@@ -344,7 +345,7 @@ int clientLogin(rcComm_t* _comm, const char* _context, const char* _scheme_overr
             // =-=-=-=-=-=-=-
             // ensure scheme is lower case for comparison
             std::string lower_scheme = auth_scheme;
-            std::transform( auth_scheme.begin(), auth_scheme.end(), auth_scheme.begin(), ::tolower );
+            std::transform( auth_scheme.begin(), auth_scheme.end(), auth_scheme.begin(), [](unsigned char _ch) { return std::tolower(_ch); });
 
             // =-=-=-=-=-=-=-
             // filter out the pam auth as it is an extra special
diff --git a/lib/core/src/irods_buffer_encryption.cpp b/lib/core/src/irods_buffer_encryption.cpp
index 7da6063f7a..5cd812f330 100644
--- a/lib/core/src/irods_buffer_encryption.cpp
+++ b/lib/core/src/irods_buffer_encryption.cpp
@@ -9,6 +9,7 @@
 #include <openssl/aes.h>
 #include <openssl/md5.h>
 
+#include <cctype>
 #include <iostream>
 #include <sstream>
 #include <iomanip>
@@ -67,7 +68,7 @@ namespace irods {
             algorithm_.begin(),
             algorithm_.end(),
             algorithm_.begin(),
-            ::tolower );
+            [](unsigned char _ch) { return std::tolower(_ch); });
 
         // =-=-=-=-=-=-=-
         // select some sane defaults
diff --git a/lib/hasher/src/checksum.cpp b/lib/hasher/src/checksum.cpp
index ddfda3840e..7e8c5e43bf 100644
--- a/lib/hasher/src/checksum.cpp
+++ b/lib/hasher/src/checksum.cpp
@@ -9,6 +9,7 @@
 #include "irods/rodsKeyWdDef.h"
 #include "irods/rcMisc.h"
 
+#include <cctype>
 #include <cstdio>
 #include <ctime>
 #include <cstring>
@@ -59,7 +60,7 @@ int chksumLocFile(
             env_scheme.begin(),
             env_scheme.end(),
             env_scheme.begin(),
-            ::tolower );
+            [](unsigned char _ch) { return std::tolower(_ch); });
     }
 
     // =-=-=-=-=-=-=-
@@ -75,7 +76,7 @@ int chksumLocFile(
             hash_scheme.begin(),
             hash_scheme.end(),
             hash_scheme.begin(),
-            ::tolower );
+            [](unsigned char _ch) { return std::tolower(_ch); });
     }
     else {
         hash_scheme = env_scheme;
@@ -88,12 +89,12 @@ int chksumLocFile(
         hash_scheme.begin(),
         hash_scheme.end(),
         hash_scheme.begin(),
-        ::tolower );
+        [](unsigned char _ch) { return std::tolower(_ch); });
     std::transform(
         env_scheme.begin(),
         env_scheme.end(),
         env_scheme.begin(),
-        ::tolower );
+        [](unsigned char _ch) { return std::tolower(_ch); });
 
 
     // =-=-=-=-=-=-=-
diff --git a/plugins/database/src/db_plugin.cpp b/plugins/database/src/db_plugin.cpp
index 275602ab17..144145eb67 100644
--- a/plugins/database/src/db_plugin.cpp
+++ b/plugins/database/src/db_plugin.cpp
@@ -2027,7 +2027,7 @@ irods::error db_debug_op(
         mode.begin(),
         mode.end(),
         mode.begin(),
-        ::tolower );
+        [](unsigned char _ch) { return std::tolower(_ch); });
 
     // =-=-=-=-=-=-=-
     // if mode contains 'sql' then turn SQL logging on
diff --git a/server/api/src/rsFileChksum.cpp b/server/api/src/rsFileChksum.cpp
index eca5ae3a3d..0cf0283c5d 100644
--- a/server/api/src/rsFileChksum.cpp
+++ b/server/api/src/rsFileChksum.cpp
@@ -16,6 +16,7 @@
 #include <fmt/format.h>
 
 #include <algorithm>
+#include <cctype>
 #include <climits>
 #include <string>
 #include <string_view>
@@ -132,7 +133,7 @@ int fileChksum(rsComm_t* rsComm,
         hash_scheme.begin(),
         hash_scheme.end(),
         hash_scheme.begin(),
-        ::tolower );
+        [](unsigned char _ch) { return std::tolower(_ch); });
 
     std::string hash_policy;
     try {
@@ -302,7 +303,7 @@ int file_checksum(RsComm* _comm,
     catch (const irods::exception&) {}
 
     // Make sure the read parameter is lowercased.
-    std::transform(hash_scheme.begin(), hash_scheme.end(), hash_scheme.begin(), ::tolower);
+    std::transform(hash_scheme.begin(), hash_scheme.end(), hash_scheme.begin(), [](unsigned char _ch) { return std::tolower(_ch); });
 
     std::string_view hash_policy;
     try {
diff --git a/server/icat/src/icatHighLevelRoutines.cpp b/server/icat/src/icatHighLevelRoutines.cpp
index 29b3e6423a..8ab4ff06db 100644
--- a/server/icat/src/icatHighLevelRoutines.cpp
+++ b/server/icat/src/icatHighLevelRoutines.cpp
@@ -25,6 +25,7 @@
 
 // =-=-=-=-=-=-=-
 // stl includes
+#include <cctype> // For std::tolower
 #include <string>
 #include <iostream>
 #include <sstream>
@@ -50,11 +51,7 @@ int chlDebug(
     // =-=-=-=-=-=-=-
     // run tolower on mode
     std::string mode( _mode );
-    std::transform(
-        mode.begin(),
-        mode.end(),
-        mode.begin(),
-        ::tolower );
+    std::transform( mode.begin(), mode.end(), mode.begin(), [](unsigned char _ch) { return std::tolower(_ch); });
 
     // =-=-=-=-=-=-=-
     // if mode contains 'sql' then turn SQL logging on