5 files changed, 9 insertions, 6 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index c9a624eeb..c72b69af2 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -22,6 +22,7 @@
 #include <algorithm>
 #include <chrono>
 #include <iostream>
+#include <sstream>
 #include <cstring>
 #include <optional>
 #include <unistd.h>
@@ -29,7 +30,6 @@
 #include <sys/resource.h>
 #include <fstream>
 #include <functional>
-#include <iostream>
 
 #include <sys/resource.h>
 #include <nlohmann/json.hpp>
diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l
index 1780f5cb9..1c1cdd673 100644
--- a/src/libexpr/lexer.l
+++ b/src/libexpr/lexer.l
@@ -26,10 +26,9 @@
 #pragma clang diagnostic ignored "-Wimplicit-fallthrough"
 #endif
 
-#include <boost/lexical_cast.hpp>
-
 #include "nixexpr.hh"
 #include "parser-tab.hh"
+#include "strings.hh"
 
 using namespace nix;
 
@@ -132,9 +131,10 @@ or          { return OR_KW; }
 
 {ID}        { yylval->id = {yytext, (size_t) yyleng}; return ID; }
 {INT}       { errno = 0;
-              try {
-                  yylval->n = boost::lexical_cast<int64_t>(yytext);
-              } catch (const boost::bad_lexical_cast &) {
+              std::optional<int64_t> numMay = string2Int<int64_t>(yytext);
+              if (numMay.has_value()) {
+                  yylval->n = *numMay;
+              } else {
                   throw ParseError(ErrorInfo{
                       .msg = HintFmt("invalid integer '%1%'", yytext),
                       .pos = state->positions[CUR_POS],
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 6a1aa8f35..664872882 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -6,6 +6,7 @@
 #include "escape-string.hh"
 
 #include <cstdlib>
+#include <sstream>
 
 namespace nix {
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index f8ce90ac1..3cc2659fb 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -25,6 +25,7 @@
 
 #include <algorithm>
 #include <cstring>
+#include <sstream>
 #include <regex>
 #include <dlfcn.h>
 
diff --git a/src/libexpr/print.cc b/src/libexpr/print.cc
index c56b0e72e..e387a09fb 100644
--- a/src/libexpr/print.cc
+++ b/src/libexpr/print.cc
@@ -1,6 +1,7 @@
 #include <limits>
 #include <span>
 #include <unordered_set>
+#include <sstream>
 
 #include "escape-string.hh"
 #include "print.hh"