diff --git a/depends/CMakeLists.txt b/depends/CMakeLists.txt
index 9ec71646a..0756519ef 100644
--- a/depends/CMakeLists.txt
+++ b/depends/CMakeLists.txt
@@ -6,14 +6,10 @@ add_subdirectory(protobuf)
 
 if(UNIX)
     set_target_properties(lua PROPERTIES COMPILE_FLAGS "-Wno-deprecated-declarations -Wno-deprecated-enum-enum-conversion")
-    target_compile_options(protoc
-        PUBLIC -Wno-deprecated-declarations -Wno-restrict)
-    target_compile_options(protoc-bin
-        PUBLIC -Wno-deprecated-declarations -Wno-restrict)
-    target_compile_options(protobuf-lite
-        PUBLIC -Wno-deprecated-declarations -Wno-restrict)
-    target_compile_options(protobuf
-        PUBLIC -Wno-deprecated-declarations -Wno-restrict)
+    set_target_properties(protoc PROPERTIES COMPILE_FLAGS "-Wno-deprecated-declarations -Wno-restrict")
+    set_target_properties(protoc-bin PROPERTIES COMPILE_FLAGS "-Wno-deprecated-declarations -Wno-restrict")
+    set_target_properties(protobuf-lite PROPERTIES COMPILE_FLAGS "-Wno-deprecated-declarations -Wno-restrict")
+    set_target_properties(protobuf PROPERTIES COMPILE_FLAGS "-Wno-deprecated-declarations -Wno-restrict")
 endif()
 
 if(UNIX AND NOT APPLE) # remove this once our MSVC build env has been updated
diff --git a/depends/protobuf/google/protobuf/repeated_field.h b/depends/protobuf/google/protobuf/repeated_field.h
index aed4ce9f2..637708254 100644
--- a/depends/protobuf/google/protobuf/repeated_field.h
+++ b/depends/protobuf/google/protobuf/repeated_field.h
@@ -46,6 +46,10 @@
 #ifndef GOOGLE_PROTOBUF_REPEATED_FIELD_H__
 #define GOOGLE_PROTOBUF_REPEATED_FIELD_H__
 
+#ifdef __GNUC__
+#pragma GCC system_header
+#endif
+
 #include <string>
 #include <iterator>
 #include <google/protobuf/stubs/common.h>
diff --git a/library/DataDefs.cpp b/library/DataDefs.cpp
index f376edc6a..cd261d50f 100644
--- a/library/DataDefs.cpp
+++ b/library/DataDefs.cpp
@@ -213,12 +213,12 @@ std::string pointer_identity::getFullName()
 
 std::string container_identity::getFullName(type_identity *item)
 {
-    return "<" + (item ? item->getFullName() : std::string("void")) + ">";
+    return '<' + (item ? item->getFullName() : std::string("void")) + '>';
 }
 
 std::string ptr_container_identity::getFullName(type_identity *item)
 {
-    return "<" + (item ? item->getFullName() : std::string("void")) + "*>";
+    return '<' + (item ? item->getFullName() : std::string("void")) + std::string("*>");
 }
 
 std::string bit_container_identity::getFullName(type_identity *)
diff --git a/library/modules/Gui.cpp b/library/modules/Gui.cpp
index d03bcce09..01fbdddf3 100644
--- a/library/modules/Gui.cpp
+++ b/library/modules/Gui.cpp
@@ -182,23 +182,23 @@ DEFINE_GET_FOCUS_STRING_HANDLER(dwarfmode)
     if (game->main_interface.info.open) {
         newFocusString = baseFocus;
         newFocusString += "/Info";
-        newFocusString += "/" + enum_item_key(game->main_interface.info.current_mode);
+        newFocusString += '/' + enum_item_key(game->main_interface.info.current_mode);
 
         switch(game->main_interface.info.current_mode) {
         case df::enums::info_interface_mode_type::CREATURES:
-            newFocusString += "/" + enum_item_key(game->main_interface.info.creatures.current_mode);
+            newFocusString += '/' + enum_item_key(game->main_interface.info.creatures.current_mode);
             break;
         case df::enums::info_interface_mode_type::BUILDINGS:
-            newFocusString += "/" + enum_item_key(game->main_interface.info.buildings.mode);
+            newFocusString += '/' + enum_item_key(game->main_interface.info.buildings.mode);
             break;
         case df::enums::info_interface_mode_type::LABOR:
-            newFocusString += "/" + enum_item_key(game->main_interface.info.labor.mode);
+            newFocusString += '/' + enum_item_key(game->main_interface.info.labor.mode);
             break;
         case df::enums::info_interface_mode_type::ARTIFACTS:
-            newFocusString += "/" + enum_item_key(game->main_interface.info.artifacts.mode);
+            newFocusString += '/' + enum_item_key(game->main_interface.info.artifacts.mode);
             break;
         case df::enums::info_interface_mode_type::JUSTICE:
-            newFocusString += "/" + enum_item_key(game->main_interface.info.justice.current_mode);
+            newFocusString += '/' + enum_item_key(game->main_interface.info.justice.current_mode);
             break;
         default:
             break;
@@ -209,7 +209,7 @@ DEFINE_GET_FOCUS_STRING_HANDLER(dwarfmode)
     if (game->main_interface.view_sheets.open) {
         newFocusString = baseFocus;
         newFocusString += "/ViewSheets";
-        newFocusString += "/" + enum_item_key(game->main_interface.view_sheets.active_sheet);
+        newFocusString += '/' + enum_item_key(game->main_interface.view_sheets.active_sheet);
         focusStrings.push_back(newFocusString);
     }
 
@@ -233,7 +233,7 @@ DEFINE_GET_FOCUS_STRING_HANDLER(dwarfmode)
             newFocusString += "/Zone";
             if (game->main_interface.civzone.cur_bld) {
                 newFocusString += "/Some";
-                newFocusString += "/" + enum_item_key(game->main_interface.civzone.cur_bld->type);
+                newFocusString += '/' + enum_item_key(game->main_interface.civzone.cur_bld->type);
             }
             break;
         case df::enums::main_bottom_mode_type::ZONE_PAINT:
@@ -499,7 +499,7 @@ DEFINE_GET_FOCUS_STRING_HANDLER(dungeonmode)
     if (!adventure)
         return;
 
-    focus += "/" + enum_item_key(adventure->menu);
+    focus += '/' + enum_item_key(adventure->menu);
 }
 */
 
@@ -1427,7 +1427,7 @@ DFHACK_EXPORT int Gui::makeAnnouncement(df::announcement_type type, df::announce
         if (flags.bits.D_DISPLAY)
         {
             world->status.display_timer = ANNOUNCE_DISPLAY_TIME;
-            Gui::writeToGamelog("x" + to_string(repeat_count + 1));
+            Gui::writeToGamelog('x' + to_string(repeat_count + 1));
         }
         return -1;
     }