diff --git a/.github/workflows/build-cppfront.yaml b/.github/workflows/build-cppfront.yaml
index 3c44d77b13..8d228b383a 100644
--- a/.github/workflows/build-cppfront.yaml
+++ b/.github/workflows/build-cppfront.yaml
@@ -9,7 +9,7 @@ jobs:
       - name: Compiler name & version
         run: cl.exe
       - name: Build
-        run: cl.exe source/cppfront.cpp -std:c++latest -MD -EHsc -experimental:module -W4
+        run: cl.exe source/cppfront.cpp -std:c++latest -MD -EHsc -experimental:module -W4 -WX
   build-unix-like:
     strategy:
       fail-fast: false
@@ -36,7 +36,7 @@ jobs:
     runs-on: ${{ matrix.runs-on }}
     env:
       CXX: ${{ matrix.compiler }}
-      CXXFLAGS: -std=${{ matrix.cxx-std }} -Wall -Wextra -Wold-style-cast -pthread
+      CXXFLAGS: -std=${{ matrix.cxx-std }} -Wall -Wextra -Wold-style-cast -Wpedantic -Werror -pthread
     steps:
     - uses: actions/checkout@v3
     - name: Install compiler
diff --git a/source/common.h b/source/common.h
index fe0301c14b..67565e1b46 100644
--- a/source/common.h
+++ b/source/common.h
@@ -65,8 +65,8 @@ struct source_line
         -> int
     {
         return
-            std::find_if_not( text.begin(), text.end(), &isspace )
-                - text.begin();
+            unsafe_narrow<int>(std::find_if_not( text.begin(), text.end(), &isspace )
+                               - text.begin());
     }
 
     auto prefix() const
@@ -334,7 +334,7 @@ auto is_nondigit(char c)
         isalpha(c)
         || c == '_'
         ;
-};
+}
 
 //G identifier-start:
 //G     nondigit
@@ -379,7 +379,7 @@ auto starts_with_identifier(std::string_view s)
         return j;
     }
     return 0;
-};
+}
 
 
 //  Helper to allow one of the above or a digit separator
@@ -759,7 +759,7 @@ class cmdline_processor
         auto length = std::ssize(name);
         if (opt_out) { length += 3; }   // space to print "[-]"
         if (max_flag_length < length) {
-            max_flag_length = length;
+            max_flag_length = unsafe_narrow<int>(length);
         }
     }
     struct register_flag {
diff --git a/source/io.h b/source/io.h
index cf016a3fd4..462f96a76d 100644
--- a/source/io.h
+++ b/source/io.h
@@ -457,7 +457,7 @@ class braces_tracker
     }
 
     auto current_depth() const -> int {
-        return std::ssize(open_braces);
+        return unsafe_narrow<int>(std::ssize(open_braces));
     }
 
     //  --- Preprocessor matching functions - #if/#else/#endif
@@ -610,7 +610,7 @@ auto process_cpp_line(
                 return r;
             }
             in_raw_string_literal = false;
-            i = end_pos+raw_string_closing_seq.size()-1;
+            i = unsafe_narrow<int>(end_pos+raw_string_closing_seq.size()-1);
         }
         else {
             r.all_comment_line = false;
@@ -797,7 +797,7 @@ auto process_cpp2_line(
 
     if (in_char_literal) {
         errors.emplace_back(
-            source_position(lineno, ssize(line)),
+            source_position(lineno, unsafe_narrow<colno_t>(ssize(line))),
             std::string("line ended before character literal was terminated")
         );
     }
@@ -957,7 +957,7 @@ class source
                             lines.back().text,
                             in_comment,
                             braces,
-                            std::ssize(lines)-1,
+                            unsafe_narrow<lineno_t>(std::ssize(lines)-1),
                             errors
                         )
                         && in.getline(&buf[0], max_line_len)
@@ -982,7 +982,7 @@ class source
                             in_raw_string_literal,
                             raw_string_closing_seq,
                             braces,
-                            std::ssize(lines) - 1
+                            unsafe_narrow<lineno_t>(std::ssize(lines)-1)
                         );
                         if (stats.all_comment_line) {
                             lines.back().cat = source_line::category::comment;
diff --git a/source/lex.h b/source/lex.h
index 478fe3da8a..f08c3eedb1 100644
--- a/source/lex.h
+++ b/source/lex.h
@@ -199,7 +199,7 @@ auto _as(lexeme l)
     break;case lexeme::None:                return "(NONE)";
     break;default:                          return "INTERNAL-ERROR";
     }
-};
+}
 
 
 auto is_operator(lexeme l)
@@ -286,13 +286,13 @@ class token
         pos.colno += offset;
     }
 
-    auto position() const -> source_position { return pos;       }
+    auto position() const -> source_position { return pos;                           }
 
-    auto length  () const -> int             { return sv.size(); }
+    auto length  () const -> int             { return unsafe_narrow<int>(sv.size()); }
 
-    auto type    () const -> lexeme          { return lex_type;  }
+    auto type    () const -> lexeme          { return lex_type;                      }
 
-    auto set_type(lexeme l) -> void          { lex_type = l;     }
+    auto set_type(lexeme l) -> void          { lex_type = l;                         }
 
     auto visit(auto& v, int depth) const
         -> void
@@ -307,7 +307,7 @@ class token
             )
         {
             sv.remove_prefix(prefix.size());
-            pos.colno += prefix.size();
+            pos.colno += unsafe_narrow<colno_t>(prefix.size());
         }
     }
 
@@ -816,7 +816,7 @@ auto lex_line(
             source_position(lineno, i + 1),
             type
             });
-        i += num-1;
+        i += unsafe_narrow<int>(num-1);
 
         merge_cpp1_multi_token_fundamental_type_names();
         merge_operator_function_names();
@@ -1066,7 +1066,7 @@ auto lex_line(
         auto parts = expand_raw_string_literal(opening_seq, closing_seq, closing_strategy, part, errors, source_position(lineno, pos_to_replace + 1));
         auto new_part = parts.generate();
         mutable_line.replace( pos_to_replace, size_to_replace, new_part );
-        i += std::ssize(new_part)-1;
+        i += unsafe_narrow<colno_t>(std::ssize(new_part)-1);
 
         if (parts.is_expanded()) {
             // raw string was expanded and we need to repeat the processing of this line
@@ -1147,7 +1147,7 @@ auto lex_line(
                 auto closing_strategy = end_pos == line.npos ? string_parts::no_ends : string_parts::on_the_end;
                 auto size_to_replace  = end_pos == line.npos ? std::ssize(line) - i  : end_pos - i + std::ssize(rsm.closing_seq);
 
-                if (interpolate_raw_string(rsm.opening_seq, rsm.closing_seq, closing_strategy, part, i, size_to_replace ) ) {
+                if (interpolate_raw_string(rsm.opening_seq, rsm.closing_seq, closing_strategy, part, i, unsafe_narrow<int>(size_to_replace) ) ) {
                     continue;
                 }
             }
@@ -1164,7 +1164,7 @@ auto lex_line(
             raw_string_multiline.value().text += raw_string_multiline.value().closing_seq;
 
             // and position where multiline_raw_string ends (needed for reseting line parsing)
-            i = end_pos+std::ssize(raw_string_multiline.value().closing_seq)-1;
+            i = unsafe_narrow<colno_t>(end_pos+std::ssize(raw_string_multiline.value().closing_seq)-1);
 
             const auto& text = raw_string_multiline.value().should_interpolate ? raw_string_multiline.value().text.substr(1) : raw_string_multiline.value().text;
             multiline_raw_strings.emplace_back(multiline_raw_string{ text, {lineno, i} });
@@ -1379,7 +1379,9 @@ auto lex_line(
                                     opening_seq,
                                     closing_seq,
                                     string_parts::on_both_ends,
-                                    std::string_view(&line[paren_pos+1], closing_pos-paren_pos-1), i, closing_pos-i+std::ssize(closing_seq))
+                                    std::string_view(&line[paren_pos+1], closing_pos-paren_pos-1),
+                                    i,
+                                    unsafe_narrow<int>(closing_pos-i+std::ssize(closing_seq)))
                             ) {
                                 continue;
                             }
@@ -1397,12 +1399,14 @@ auto lex_line(
                                     opening_seq,
                                     closing_seq,
                                     string_parts::on_the_beginning,
-                                    std::string_view(&line[paren_pos+1], std::ssize(line)-(paren_pos+1)), i, std::ssize(line)-i)
+                                    std::string_view(&line[paren_pos+1], std::ssize(line)-(paren_pos+1)),
+                                    i,
+                                    unsafe_narrow<int>(std::ssize(line)-i))
                             ) {
                                 continue;
                             }
                             // skip entire raw string opening sequence R"
-                            i = paren_pos;
+                            i = unsafe_narrow<int>(paren_pos);
 
                             // if we are on the end of the line we need to add new line char
                             if (i+1 == std::ssize(line)) {
@@ -1594,7 +1598,7 @@ auto lex_line(
                             } else {
                                 raw_string_multiline.emplace(raw_string{source_position{lineno, i}, opening_seq, opening_seq, closing_seq });
                                 // skip entire raw string opening sequence R"
-                                i = paren_pos;
+                                i = unsafe_narrow<int>(paren_pos);
 
                                 // if we are on the end of the line we need to add new line char
                                 if (i+1 == std::ssize(line)) {
@@ -1842,7 +1846,7 @@ class tokens
 
             //  Create new map entry for the section starting at this line,
             //  and populate its tokens with the tokens in this section
-            auto lineno = std::distance(std::begin(lines), line);
+            auto lineno = unsafe_narrow<lineno_t>(std::distance(std::begin(lines), line));
 
             //  If this is generated code, use negative line numbers to
             //  inform and assist the printer
diff --git a/source/parse.h b/source/parse.h
index 3ac3555c48..df067fb49a 100644
--- a/source/parse.h
+++ b/source/parse.h
@@ -322,7 +322,7 @@ struct binary_expression_node
     auto terms_size() const
         -> int
     {
-        return std::ssize(terms);
+        return unsafe_narrow<int>(std::ssize(terms));
     }
 
     auto is_identifier() const
@@ -2313,7 +2313,7 @@ struct function_type_node
     auto parameter_count() const
         -> int
     {
-        return std::ssize(parameters->parameters);
+        return unsafe_narrow<int>(std::ssize(parameters->parameters));
     }
 
     auto index_of_parameter_named(std::string_view s) const
@@ -5785,7 +5785,7 @@ class parser
         }
 
         for (auto& e : expression_node::current_expressions) {
-            e->num_subexpressions += std::ssize(n->ops);
+            e->num_subexpressions += unsafe_narrow<int>(std::ssize(n->ops));
         }
 
         return n;
diff --git a/source/sema.h b/source/sema.h
index d339659cd2..6c96b70aaf 100644
--- a/source/sema.h
+++ b/source/sema.h
@@ -546,7 +546,7 @@ class sema
         //-----------------------------------------------------------------------
         //  Function logic: For each entry in the table...
         //
-        for (auto sympos = std::ssize(symbols) - 1; sympos >= 0; --sympos)
+        for (auto sympos = unsafe_narrow<int>(std::ssize(symbols) - 1); sympos >= 0; --sympos)
         {
             //  If this is an uninitialized local variable,
             //  ensure it is definitely initialized and tag those initializations
diff --git a/source/to_cpp1.h b/source/to_cpp1.h
index a40589d3a9..502d95c394 100644
--- a/source/to_cpp1.h
+++ b/source/to_cpp1.h
@@ -402,11 +402,11 @@ class positional_printer
             //  Now also adjust the colno
             if (last_newline != std::string::npos) {
                 //  If we found a newline, it's the distance from the last newline to EOL
-                curr_pos.colno = s.length() - last_newline;
+                curr_pos.colno = unsafe_narrow<colno_t>(s.length() - last_newline);
             }
             else {
                 //  Else add the length of the string
-                curr_pos.colno += s.length();
+                curr_pos.colno += unsafe_narrow<colno_t>(s.length());
             }
         }
     }
@@ -2777,7 +2777,7 @@ class cppfront
             return is_pointer_declaration(type_id_node->address_of, deref_cnt, addr_cnt + 1);
         }
 
-        int pointer_declarators_cnt = std::count_if(std::cbegin(type_id_node->pc_qualifiers), std::cend(type_id_node->pc_qualifiers), [](auto* q) {
+        auto pointer_declarators_cnt = std::count_if(std::cbegin(type_id_node->pc_qualifiers), std::cend(type_id_node->pc_qualifiers), [](auto* q) {
             return q->type() == lexeme::Multiply;
         });
 
@@ -2789,7 +2789,7 @@ class cppfront
             return is_pointer_declaration(type_id_node->suspicious_initialization, deref_cnt, addr_cnt);
         }
 
-        return (pointer_declarators_cnt + addr_cnt - deref_cnt) > 0;
+        return (unsafe_narrow<int>(pointer_declarators_cnt) + addr_cnt - deref_cnt) > 0;
     }
 
     auto is_pointer_declaration(