diff --git a/doc/external-api/local.mk b/doc/external-api/local.mk
index a0f6e26fc..aa501198b 100644
--- a/doc/external-api/local.mk
+++ b/doc/external-api/local.mk
@@ -1,19 +1,19 @@
 .PHONY: external-api-html
 
-ifeq ($(internal_api_docs), yes)
+ifeq ($(external_api_docs), yes)
 
 $(docdir)/external-api/html/index.html $(docdir)/external-api/latex: $(d)/doxygen.cfg
 	mkdir -p $(docdir)/external-api
 	{ cat $< ; echo "OUTPUT_DIRECTORY=$(docdir)/external-api" ; } | doxygen -
 
-# Generate the HTML API docs for Nix's unstable internal interfaces.
+# Generate the HTML API docs for Nix's unstable external interfaces.
 external-api-html: $(docdir)/external-api/html/index.html
 
 else
 
 # Make a nicer error message
 external-api-html:
-	@echo "Internal API docs are disabled. Configure with '--enable-external-api-docs', or avoid calling 'make external-api-html'."
+	@echo "External API docs are disabled. Configure with '--enable-external-api-docs', or avoid calling 'make external-api-html'."
 	@exit 1
 
 endif
diff --git a/flake.nix b/flake.nix
index 89b928e83..be4e68783 100644
--- a/flake.nix
+++ b/flake.nix
@@ -285,6 +285,13 @@
           enableInternalAPIDocs = true;
         };
 
+        # API docs for Nix's C bindings.
+        external-api-docs = nixpkgsFor.x86_64-linux.native.callPackage ./package.nix {
+          inherit fileset;
+          doBuild = false;
+          enableExternalAPIDocs = true;
+        };
+
         # System tests.
         tests = import ./tests/nixos { inherit lib nixpkgs nixpkgsFor; } // {
 
diff --git a/package.nix b/package.nix
index a334ae48c..af4ca9b46 100644
--- a/package.nix
+++ b/package.nix
@@ -5,6 +5,7 @@
 , autoreconfHook
 , aws-sdk-cpp
 , boehmgc
+, buildPackages
 , nlohmann_json
 , bison
 , boost
@@ -91,9 +92,10 @@
 # - readline
 , readlineFlavor ? if stdenv.hostPlatform.isWindows then "readline" else "editline"
 
-# Whether to build the internal API docs, can be done separately from
+# Whether to build the internal/external API docs, can be done separately from
 # everything else.
 , enableInternalAPIDocs ? false
+, enableExternalAPIDocs ? false
 
 # Whether to install unit tests. This is useful when cross compiling
 # since we cannot run them natively during the build, but can do so
@@ -199,7 +201,7 @@ in {
     ++ lib.optional doBuild "dev"
     # If we are doing just build or just docs, the one thing will use
     # "out". We only need additional outputs if we are doing both.
-    ++ lib.optional (doBuild && (enableManual || enableInternalAPIDocs)) "doc"
+    ++ lib.optional (doBuild && (enableManual || enableInternalAPIDocs || enableExternalAPIDocs)) "doc"
     ++ lib.optional installUnitTests "check";
 
   nativeBuildInputs = [
@@ -221,7 +223,7 @@ in {
   ] ++ lib.optionals (doInstallCheck || enableManual) [
     jq # Also for custom mdBook preprocessor.
   ] ++ lib.optional stdenv.hostPlatform.isLinux util-linux
-    ++ lib.optional enableInternalAPIDocs doxygen
+    ++ lib.optional (enableInternalAPIDocs || enableExternalAPIDocs) doxygen
   ;
 
   buildInputs = lib.optionals doBuild [
@@ -285,6 +287,7 @@ in {
     (lib.enableFeature buildUnitTests "unit-tests")
     (lib.enableFeature doInstallCheck "functional-tests")
     (lib.enableFeature enableInternalAPIDocs "internal-api-docs")
+    (lib.enableFeature enableExternalAPIDocs "external-api-docs")
     (lib.enableFeature enableManual "doc-gen")
     (lib.enableFeature enableGC "gc")
     (lib.enableFeature enableMarkdown "markdown")
@@ -309,7 +312,8 @@ in {
   makeFlags = "profiledir=$(out)/etc/profile.d PRECOMPILE_HEADERS=1";
 
   installTargets = lib.optional doBuild "install"
-    ++ lib.optional enableInternalAPIDocs "internal-api-html";
+    ++ lib.optional enableInternalAPIDocs "internal-api-html"
+    ++ lib.optional enableExternalAPIDocs "external-api-html";
 
   installFlags = "sysconfdir=$(out)/etc";
 
@@ -336,6 +340,10 @@ in {
   '' + lib.optionalString enableInternalAPIDocs ''
     mkdir -p ''${!outputDoc}/nix-support
     echo "doc internal-api-docs $out/share/doc/nix/internal-api/html" >> ''${!outputDoc}/nix-support/hydra-build-products
+  ''
+    + lib.optionalString enableExternalAPIDocs ''
+    mkdir -p ''${!outputDoc}/nix-support
+    echo "doc external-api-docs $out/share/doc/nix/external-api/html" >> ''${!outputDoc}/nix-support/hydra-build-products
   '';
 
   # So the check output gets links for DLLs in the out output.