diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index 53103832162..940b16dfdfd 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -57,9 +57,7 @@ enum class ProcessLineResult {
 struct NixRepl
     : AbstractNixRepl
     , detail::ReplCompleterMixin
-    #if HAVE_BOEHMGC
     , gc
-    #endif
 {
     size_t debugTraceIndex;
 
diff --git a/src/libexpr/eval-gc.hh b/src/libexpr/eval-gc.hh
index 58436584496..8f492c56d8c 100644
--- a/src/libexpr/eval-gc.hh
+++ b/src/libexpr/eval-gc.hh
@@ -13,12 +13,19 @@
 
 #else
 
+/* Some dummy aliases for Boehm GC definitions to reduce the number of
+   #ifdefs. */
+
 template<typename T>
 using traceable_allocator = std::allocator<T>;
 
 template<typename T>
 using gc_allocator = std::allocator<T>;
 
+#define GC_MALLOC_ATOMIC std::malloc
+#define GC_STRDUP std::strdup
+struct gc { };
+
 #endif
 
 namespace nix {
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 5952ebe41ff..379839ce32f 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -47,11 +47,7 @@ namespace nix {
 static char * allocString(size_t size)
 {
     char * t;
-#if HAVE_BOEHMGC
     t = (char *) GC_MALLOC_ATOMIC(size);
-#else
-    t = (char *) malloc(size);
-#endif
     if (!t) throw std::bad_alloc();
     return t;
 }
@@ -60,11 +56,7 @@ static char * allocString(size_t size)
 static char * dupString(const char * s)
 {
     char * t;
-#if HAVE_BOEHMGC
     t = GC_STRDUP(s);
-#else
-    t = strdup(s);
-#endif
     if (!t) throw std::bad_alloc();
     return t;
 }