diff --git a/src/env.cpp b/src/env.cpp
index 6d7143b42..ba85aaada 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -33,6 +33,7 @@
 #include "proc.h"
 #include "reader.h"
 #include "termsize.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Some configuration path environment variables.
diff --git a/src/exec.cpp b/src/exec.cpp
index af7f11085..57393b24f 100644
--- a/src/exec.cpp
+++ b/src/exec.cpp
@@ -48,6 +48,7 @@
 #include "signal.h"
 #include "timer.h"
 #include "trace.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Number of calls to fork() or posix_spawn().
diff --git a/src/flog.cpp b/src/flog.cpp
index 1a64ef228..d1e8b076a 100644
--- a/src/flog.cpp
+++ b/src/flog.cpp
@@ -46,6 +46,10 @@ void logger_t::log1(wchar_t c) { std::fputwc(c, file_); }
 
 void logger_t::log1(char c) { std::fwprintf(file_, L"%c", c); }
 
+void logger_t::log1(int64_t v) { std::fwprintf(file_, L"%lld", v); }
+
+void logger_t::log1(uint64_t v) { std::fwprintf(file_, L"%llu", v); }
+
 void logger_t::log_fmt(const category_t &cat, const wchar_t *fmt, ...) {
     va_list va;
     va_start(va, fmt);
diff --git a/src/flog.h b/src/flog.h
index eed0c0771..30bdb4cb8 100644
--- a/src/flog.h
+++ b/src/flog.h
@@ -11,7 +11,6 @@
 #include <utility>
 
 #include "global_safety.h"
-#include "wcstringutil.h"
 
 using wcstring = std::wstring;
 using wcstring_list_t = std::vector<wcstring>;
@@ -115,14 +114,20 @@ class logger_t {
     void log1(const char *);
     void log1(wchar_t);
     void log1(char);
+    void log1(int64_t);
+    void log1(uint64_t);
 
     void log1(const wcstring &s) { log1(s.c_str()); }
     void log1(const std::string &s) { log1(s.c_str()); }
 
     template <typename T,
               typename Enabler = typename std::enable_if<std::is_integral<T>::value>::type>
-    void log1(const T &v) {
-        log1(to_string(v));
+    void log1(T v) {
+        if (std::is_signed<T>::value) {
+            log1(static_cast<int64_t>(v));
+        } else {
+            log1(static_cast<uint64_t>(v));
+        }
     }
 
     template <typename T>
diff --git a/src/path.cpp b/src/path.cpp
index 570d06a44..79f7ad980 100644
--- a/src/path.cpp
+++ b/src/path.cpp
@@ -21,6 +21,7 @@
 #include "expand.h"
 #include "fallback.h"  // IWYU pragma: keep
 #include "flog.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Unexpected error in path_get_path().
diff --git a/src/proc.cpp b/src/proc.cpp
index a44ef90d8..e09ba5825 100644
--- a/src/proc.cpp
+++ b/src/proc.cpp
@@ -51,6 +51,7 @@
 #include "reader.h"
 #include "sanity.h"
 #include "signal.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 /// The signals that signify crashes to us.
diff --git a/src/termsize.cpp b/src/termsize.cpp
index 905d922ff..cf3591adf 100644
--- a/src/termsize.cpp
+++ b/src/termsize.cpp
@@ -4,6 +4,7 @@
 
 #include "maybe.h"
 #include "parser.h"
+#include "wcstringutil.h"
 #include "wutil.h"
 
 // A counter which is incremented every SIGWINCH, or when the tty is otherwise invalidated.
diff --git a/src/wutil.cpp b/src/wutil.cpp
index c79c3073d..f046acfac 100644
--- a/src/wutil.cpp
+++ b/src/wutil.cpp
@@ -29,6 +29,7 @@
 #include "common.h"
 #include "fallback.h"  // IWYU pragma: keep
 #include "flog.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 using cstring = std::string;