diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 2eec3ca2b67..3102d3a73a0 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -1732,13 +1732,20 @@ void LocalDerivationGoal::runChild()
 
         bool setUser = true;
 
-        /* Make the contents of netrc available to builtin:fetchurl
-           (which may run under a different uid and/or in a sandbox). */
+        /* Make the contents of netrc and the CA certificate bundle
+           available to builtin:fetchurl (which may run under a
+           different uid and/or in a sandbox). */
         std::string netrcData;
-        try {
-            if (drv->isBuiltin() && drv->builder == "builtin:fetchurl")
-                netrcData = readFile(settings.netrcFile);
-        } catch (SystemError &) { }
+        std::string caFileData;
+        if (drv->isBuiltin() && drv->builder == "builtin:fetchurl") {
+           try {
+               netrcData = readFile(settings.netrcFile);
+           } catch (SystemError &) { }
+
+           try {
+               caFileData = readFile(settings.caFile);
+           } catch (SystemError &) { }
+        }
 
 #if __linux__
         if (useChroot) {
@@ -2166,7 +2173,11 @@ void LocalDerivationGoal::runChild()
                     e.second = rewriteStrings(e.second, inputRewrites);
 
                 if (drv->builder == "builtin:fetchurl")
+<<<<<<< HEAD:src/libstore/build/local-derivation-goal.cc
                     builtinFetchurl(drv2, netrcData);
+=======
+                    builtinFetchurl(*drv, outputs, netrcData, caFileData);
+>>>>>>> c1ecf0bee (fix passing CA files into builtins:fetchurl sandbox):src/libstore/unix/build/local-derivation-goal.cc
                 else if (drv->builder == "builtin:buildenv")
                     builtinBuildenv(drv2);
                 else if (drv->builder == "builtin:unpack-channel")
diff --git a/src/libstore/builtins.hh b/src/libstore/builtins.hh
index d201fb3ac5b..2fef918b0aa 100644
--- a/src/libstore/builtins.hh
+++ b/src/libstore/builtins.hh
@@ -6,7 +6,19 @@
 namespace nix {
 
 // TODO: make pluggable.
+<<<<<<< HEAD
 void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData);
 void builtinUnpackChannel(const BasicDerivation & drv);
+=======
+void builtinFetchurl(
+    const BasicDerivation & drv,
+    const std::map<std::string, Path> & outputs,
+    const std::string & netrcData,
+    const std::string & caFileData);
+
+void builtinUnpackChannel(
+    const BasicDerivation & drv,
+    const std::map<std::string, Path> & outputs);
+>>>>>>> c1ecf0bee (fix passing CA files into builtins:fetchurl sandbox)
 
 }
diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc
index 3f4a3076e97..071355b5eba 100644
--- a/src/libstore/builtins/fetchurl.cc
+++ b/src/libstore/builtins/fetchurl.cc
@@ -6,7 +6,15 @@
 
 namespace nix {
 
+<<<<<<< HEAD
 void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
+=======
+void builtinFetchurl(
+    const BasicDerivation & drv,
+    const std::map<std::string, Path> & outputs,
+    const std::string & netrcData,
+    const std::string & caFileData)
+>>>>>>> c1ecf0bee (fix passing CA files into builtins:fetchurl sandbox)
 {
     /* Make the host's netrc data available. Too bad curl requires
        this to be stored in a file. It would be nice if we could just
@@ -16,6 +24,9 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
         writeFile(settings.netrcFile, netrcData, 0600);
     }
 
+    settings.caFile = "ca-certificates.crt";
+    writeFile(settings.caFile, caFileData, 0600);
+
     auto out = get(drv.outputs, "out");
     if (!out)
         throw Error("'builtin:fetchurl' requires an 'out' output");
diff --git a/tests/nixos/fetchurl.nix b/tests/nixos/fetchurl.nix
index 476f779bcc3..243c0cacc6e 100644
--- a/tests/nixos/fetchurl.nix
+++ b/tests/nixos/fetchurl.nix
@@ -1,7 +1,7 @@
 # Test whether builtin:fetchurl properly performs TLS certificate
 # checks on HTTPS servers.
 
-{ lib, config, pkgs, ... }:
+{ pkgs, ... }:
 
 let
 
@@ -25,7 +25,7 @@ in
   name = "nss-preload";
 
   nodes = {
-    machine = { lib, pkgs, ... }: {
+    machine = { pkgs, ... }: {
       services.nginx = {
         enable = true;
 
@@ -60,13 +60,16 @@ in
     };
   };
 
-  testScript = { nodes, ... }: ''
+  testScript = ''
     machine.wait_for_unit("nginx")
     machine.wait_for_open_port(443)
 
     out = machine.succeed("curl https://good/index.html")
     assert out == "hello world\n"
 
+    out = machine.succeed("cat ${badCert}/cert.pem > /tmp/cafile.pem; curl --cacert /tmp/cafile.pem https://bad/index.html")
+    assert out == "foobar\n"
+
     # Fetching from a server with a trusted cert should work.
     machine.succeed("nix build --no-substitute --expr 'import <nix/fetchurl.nix> { url = \"https://good/index.html\"; hash = \"sha256-qUiQTy8PR5uPgZdpSzAYSw0u0cHNKh7A+4XSmaGSpEc=\"; }'")
 
@@ -74,5 +77,8 @@ in
     err = machine.fail("nix build --no-substitute --expr 'import <nix/fetchurl.nix> { url = \"https://bad/index.html\"; hash = \"sha256-rsBwZF/lPuOzdjBZN2E08FjMM3JHyXit0Xi2zN+wAZ8=\"; }' 2>&1")
     print(err)
     assert "SSL certificate problem: self-signed certificate" in err
+
+    # Fetching from a server with a trusted cert should work via environment variable override.
+    machine.succeed("NIX_SSL_CERT_FILE=/tmp/cafile.pem nix build --no-substitute --expr 'import <nix/fetchurl.nix> { url = \"https://bad/index.html\"; hash = \"sha256-rsBwZF/lPuOzdjBZN2E08FjMM3JHyXit0Xi2zN+wAZ8=\"; }'")
   '';
 }