diff --git a/config/check_vanilla_allocations.py b/config/check_vanilla_allocations.py
index cb04144d5bc8..8fbef54a1584 100644
--- a/config/check_vanilla_allocations.py
+++ b/config/check_vanilla_allocations.py
@@ -165,6 +165,10 @@ def main():
         if "intl_components" in filename:
             continue
 
+        # Ignore use of std::string in regexp AST debug output.
+        if filename == "regexp-ast.o":
+            continue
+
         fn = m.group(2)
         if filename == "Utility.o":
             util_Utility_cpp.add(fn)
diff --git a/js/src/irregexp/moz.build b/js/src/irregexp/moz.build
index 900e17e7c9ef..24c0a2d4681e 100644
--- a/js/src/irregexp/moz.build
+++ b/js/src/irregexp/moz.build
@@ -15,7 +15,6 @@ include("../js-cxxflags.mozbuild")
 CXXFLAGS += ["-Wno-error=type-limits"]
 
 UNIFIED_SOURCES += [
-    "imported/regexp-ast.cc",
     "imported/regexp-bytecode-generator.cc",
     "imported/regexp-bytecode-peephole.cc",
     "imported/regexp-bytecodes.cc",
@@ -31,6 +30,7 @@ UNIFIED_SOURCES += [
     "util/UnicodeShim.cpp",
 ]
 SOURCES += [
+    "imported/regexp-ast.cc",
     "imported/regexp-compiler.cc",  # Bug 1643693
     "RegExpNativeMacroAssembler.cpp",
 ]