diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 3d8d9b8ad7..d82cc5870a 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -5,6 +5,7 @@
 #include "eval.hh"
 #include "globals.hh"
 #include "nixexpr-ast.hh"
+#include "expr-to-xml.hh"
 
 
 static Expr primBuiltins(EvalState & state, const ATermVector & args)
@@ -457,6 +458,14 @@ static Expr primToString(EvalState & state, const ATermVector & args)
 }
 
 
+static Expr primToXML(EvalState & state, const ATermVector & args)
+{
+    ostringstream out;
+    printTermAsXML(strictEvalExpr(state, args[0]), out);
+    return makeStr(toATerm(out.str()));
+}
+
+
 /* Boolean constructors. */
 static Expr primTrue(EvalState & state, const ATermVector & args)
 {
@@ -705,6 +714,7 @@ void EvalState::addPrimOps()
     addPrimOp("baseNameOf", 1, primBaseNameOf);
     addPrimOp("dirOf", 1, primDirOf);
     addPrimOp("toString", 1, primToString);
+    addPrimOp("__toXML", 1, primToXML);
     addPrimOp("isNull", 1, primIsNull);
     addPrimOp("dependencyClosure", 1, primDependencyClosure);
     addPrimOp("abort", 1, primAbort);
diff --git a/tests/lang/eval-okay-to-xml.exp b/tests/lang/eval-okay-to-xml.exp
new file mode 100644
index 0000000000..ee7d4c7d32
--- /dev/null
+++ b/tests/lang/eval-okay-to-xml.exp
@@ -0,0 +1 @@
+Str("<?xml version='1.0' encoding='utf-8'?>\n<expr>\n  <list>\n    <string value=\"ab\" />\n    <int value=\"10\" />\n    <attrs>\n      <attr name=\"x\">\n        <string value=\"x\" />\n      </attr>\n      <attr name=\"y\">\n        <string value=\"x\" />\n      </attr>\n    </attrs>\n  </list>\n</expr>\n")
diff --git a/tests/lang/eval-okay-to-xml.nix b/tests/lang/eval-okay-to-xml.nix
new file mode 100644
index 0000000000..ff1791b30e
--- /dev/null
+++ b/tests/lang/eval-okay-to-xml.nix
@@ -0,0 +1 @@
+builtins.toXML [("a" + "b") 10 (rec {x = "x"; y = x;})]