diff --git a/Libraries/LibDiff/Format.cpp b/Libraries/LibDiff/Format.cpp
index b6ee7d172b..38766b89cb 100644
--- a/Libraries/LibDiff/Format.cpp
+++ b/Libraries/LibDiff/Format.cpp
@@ -34,7 +34,7 @@ String generate_only_additions(const String& text)
 {
     auto lines = text.split('\n', true); // Keep empty
     StringBuilder builder;
-    builder.appendf("@@ -1,%zu +1,%zu @@\n", lines.size());
+    builder.appendf("@@ -0,0 +1,%zu @@\n", lines.size());
     for (const auto& line : lines) {
         builder.appendf("+%s\n", line.characters());
     }
diff --git a/Libraries/LibGfx/Triangle.cpp b/Libraries/LibGfx/Triangle.cpp
index f5fcab2047..d326b59f1c 100644
--- a/Libraries/LibGfx/Triangle.cpp
+++ b/Libraries/LibGfx/Triangle.cpp
@@ -31,7 +31,7 @@ namespace Gfx {
 
 String Triangle::to_string() const
 {
-    return String::format("({},{},{})", m_a, m_b, m_c);
+    return String::formatted("({},{},{})", m_a, m_b, m_c);
 }
 
 const LogStream& operator<<(const LogStream& stream, const Triangle& value)
diff --git a/Services/DHCPClient/DHCPv4.h b/Services/DHCPClient/DHCPv4.h
index 68bfd36171..a773167683 100644
--- a/Services/DHCPClient/DHCPv4.h
+++ b/Services/DHCPClient/DHCPv4.h
@@ -173,7 +173,7 @@ struct ParsedDHCPv4Options {
     {
         StringBuilder builder;
         builder.append("DHCP Options (");
-        builder.appendf("%d", options.size());
+        builder.appendf("%zu", options.size());
         builder.append(" entries)\n");
         for (auto& opt : options) {
             builder.appendf("\toption %d (%d bytes):", (u8)opt.key, (u8)opt.value.length);
diff --git a/Services/SystemServer/main.cpp b/Services/SystemServer/main.cpp
index f243032b95..6409b0eda6 100644
--- a/Services/SystemServer/main.cpp
+++ b/Services/SystemServer/main.cpp
@@ -130,7 +130,7 @@ static void prepare_devfs()
 
     for (size_t index = 0; index < 4; index++) {
         // FIXME: Find a better way to chown without hardcoding the gid!
-        rc = chown(String::format("/dev/tty%d", index).characters(), 0, 2);
+        rc = chown(String::formatted("/dev/tty{}", index).characters(), 0, 2);
         if (rc < 0) {
             ASSERT_NOT_REACHED();
         }
@@ -138,7 +138,7 @@ static void prepare_devfs()
 
     for (size_t index = 0; index < 4; index++) {
         // FIXME: Find a better way to chown without hardcoding the gid!
-        rc = chown(String::format("/dev/ttyS%d", index).characters(), 0, 2);
+        rc = chown(String::formatted("/dev/ttyS{}", index).characters(), 0, 2);
         if (rc < 0) {
             ASSERT_NOT_REACHED();
         }
diff --git a/Services/TelnetServer/Command.h b/Services/TelnetServer/Command.h
index ac696c2111..25afb1fe22 100644
--- a/Services/TelnetServer/Command.h
+++ b/Services/TelnetServer/Command.h
@@ -73,7 +73,7 @@ struct Command {
             builder.append("SUPPRESS_GO_AHEAD");
             break;
         default:
-            builder.append(String::format("UNKNOWN<%02x>"));
+            builder.append(String::format("UNKNOWN<%02x>", subcommand));
             break;
         }
 
diff --git a/Services/WebServer/Client.cpp b/Services/WebServer/Client.cpp
index 84ba323d64..c3840bd118 100644
--- a/Services/WebServer/Client.cpp
+++ b/Services/WebServer/Client.cpp
@@ -227,7 +227,7 @@ void Client::handle_directory_listing(const String& requested_path, const String
         builder.append(escape_html_entities(name));
         builder.append("</a></td><td>&nbsp;</td>");
 
-        builder.appendf("<td>%10d</td><td>&nbsp;</td>", st.st_size);
+        builder.appendf("<td>%10zd</td><td>&nbsp;</td>", st.st_size);
         builder.append("<td>");
         builder.append(Core::DateTime::from_timestamp(st.st_mtime).to_string());
         builder.append("</td>");
diff --git a/Userland/gunzip.cpp b/Userland/gunzip.cpp
index cf0d473850..58678d1b88 100644
--- a/Userland/gunzip.cpp
+++ b/Userland/gunzip.cpp
@@ -57,7 +57,7 @@ int main(int argc, char** argv)
 
     for (String filename : filenames) {
         if (!filename.ends_with(".gz"))
-            filename = String::format("%s.gz", filename);
+            filename = String::format("%s.gz", filename.characters());
 
         const auto input_filename = filename;
         const auto output_filename = filename.substring_view(0, filename.length() - 3);
diff --git a/Userland/w.cpp b/Userland/w.cpp
index 7e38137276..4c9dbc106b 100644
--- a/Userland/w.cpp
+++ b/Userland/w.cpp
@@ -107,7 +107,7 @@ int main()
         if (stat(tty.characters(), &st) == 0) {
             auto idle_time = now - st.st_mtime;
             if (idle_time >= 0) {
-                builder.appendf("%ds", idle_time);
+                builder.appendf("%llds", idle_time);
                 idle_string = builder.to_string();
             }
         }
diff --git a/Userland/watch.cpp b/Userland/watch.cpp
index 5188685e08..1377a7667c 100644
--- a/Userland/watch.cpp
+++ b/Userland/watch.cpp
@@ -45,7 +45,7 @@ static volatile pid_t child_pid = -1;
 static String build_header_string(const Vector<const char*>& command, const struct timeval& interval)
 {
     StringBuilder builder;
-    builder.appendf("Every %d", interval.tv_sec);
+    builder.appendff("Every {}", interval.tv_sec);
     builder.appendf(".%ds: \x1b[1m", interval.tv_usec / 100000);
     builder.join(' ', command);
     builder.append("\x1b[0m");