diff --git a/src/libstore/builtins/buildenv.cc b/src/libstore/builtins/buildenv.cc
index eeaccb24c..204912278 100644
--- a/src/libstore/builtins/buildenv.cc
+++ b/src/libstore/builtins/buildenv.cc
@@ -1,4 +1,5 @@
 #include "nix/store/builtins/buildenv.hh"
+#include "nix/store/builtins.hh"
 #include "nix/store/derivations.hh"
 #include "nix/util/signals.hh"
 
@@ -166,7 +167,7 @@ void buildProfile(const Path & out, Packages && pkgs)
     debug("created %d symlinks in user environment", state.symlinks);
 }
 
-void builtinBuildenv(
+static void builtinBuildenv(
     const BasicDerivation & drv,
     const std::map<std::string, Path> & outputs)
 {
@@ -203,4 +204,6 @@ void builtinBuildenv(
     createSymlink(getAttr("manifest"), out + "/manifest.nix");
 }
 
+static RegisterBuiltinBuilder registerBuildenv("buildenv", builtinBuildenv);
+
 }
diff --git a/src/libstore/builtins/unpack-channel.cc b/src/libstore/builtins/unpack-channel.cc
index e03f3076b..47bf25fbf 100644
--- a/src/libstore/builtins/unpack-channel.cc
+++ b/src/libstore/builtins/unpack-channel.cc
@@ -3,7 +3,7 @@
 
 namespace nix {
 
-void builtinUnpackChannel(
+static void builtinUnpackChannel(
     const BasicDerivation & drv,
     const std::map<std::string, Path> & outputs)
 {
@@ -42,4 +42,6 @@ void builtinUnpackChannel(
     }
 }
 
+static RegisterBuiltinBuilder registerUnpackChannel("unpack-channel", builtinUnpackChannel);
+
 }
diff --git a/src/libstore/include/nix/store/builtins.hh b/src/libstore/include/nix/store/builtins.hh
index 004e9ef64..6d54c2a22 100644
--- a/src/libstore/include/nix/store/builtins.hh
+++ b/src/libstore/include/nix/store/builtins.hh
@@ -12,8 +12,19 @@ void builtinFetchurl(
     const std::string & netrcData,
     const std::string & caFileData);
 
-void builtinUnpackChannel(
-    const BasicDerivation & drv,
-    const std::map<std::string, Path> & outputs);
+using BuiltinBuilder =
+    std::function<void(const BasicDerivation & drv, const std::map<std::string, Path> & outputs)>;
+
+struct RegisterBuiltinBuilder
+{
+    typedef std::map<std::string, BuiltinBuilder> BuiltinBuilders;
+    static BuiltinBuilders * builtinBuilders;
+
+    RegisterBuiltinBuilder(const std::string & name, BuiltinBuilder && fun)
+    {
+        if (!builtinBuilders) builtinBuilders = new BuiltinBuilders;
+        builtinBuilders->insert_or_assign(name, std::move(fun));
+    }
+};
 
 }
diff --git a/src/libstore/include/nix/store/builtins/buildenv.hh b/src/libstore/include/nix/store/builtins/buildenv.hh
index a0a262037..163666c0b 100644
--- a/src/libstore/include/nix/store/builtins/buildenv.hh
+++ b/src/libstore/include/nix/store/builtins/buildenv.hh
@@ -45,8 +45,4 @@ typedef std::vector<Package> Packages;
 
 void buildProfile(const Path & out, Packages && pkgs);
 
-void builtinBuildenv(
-    const BasicDerivation & drv,
-    const std::map<std::string, Path> & outputs);
-
 }
diff --git a/src/libstore/unix/build/derivation-builder.cc b/src/libstore/unix/build/derivation-builder.cc
index 4bde9750d..c40d5251b 100644
--- a/src/libstore/unix/build/derivation-builder.cc
+++ b/src/libstore/unix/build/derivation-builder.cc
@@ -1835,6 +1835,9 @@ void setupSeccomp()
 }
 
 
+RegisterBuiltinBuilder::BuiltinBuilders * RegisterBuiltinBuilder::builtinBuilders = nullptr;
+
+
 void DerivationBuilderImpl::runChild()
 {
     /* Warning: in the child we should absolutely not make any SQLite
@@ -2293,12 +2296,14 @@ void DerivationBuilderImpl::runChild()
 
                 if (drv.builder == "builtin:fetchurl")
                     builtinFetchurl(drv, outputs, netrcData, caFileData);
-                else if (drv.builder == "builtin:buildenv")
-                    builtinBuildenv(drv, outputs);
-                else if (drv.builder == "builtin:unpack-channel")
-                    builtinUnpackChannel(drv, outputs);
-                else
-                    throw Error("unsupported builtin builder '%1%'", drv.builder.substr(8));
+                else {
+                    std::string builtinName = drv.builder.substr(8);
+                    assert(RegisterBuiltinBuilder::builtinBuilders);
+                    if (auto builtin = get(*RegisterBuiltinBuilder::builtinBuilders, builtinName))
+                        (*builtin)(drv, outputs);
+                    else
+                        throw Error("unsupported builtin builder '%1%'", builtinName);
+                }
                 _exit(0);
             } catch (std::exception & e) {
                 writeFull(STDERR_FILENO, e.what() + std::string("\n"));