diff --git a/CMakeLists.txt b/CMakeLists.txt
index 74d8582..d174ec7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -51,6 +51,10 @@ macro(warnings_high)
   endif()
 endmacro()
 
+macro(oe_simulate target)
+  target_compile_definitions(${target} PRIVATE IS_REALLY_ADDRESS_SPACE_CONSTRAINED)
+endmacro()
+
 macro(clangformat_targets)
   # The clang-format tool is installed under a variety of different names.  Try
   # to find a sensible one.  Only look for versions 9 explicitly - we don't
@@ -244,6 +248,9 @@ if(NOT DEFINED SNMALLOC_ONLY_HEADER_LIBRARY)
     add_shim(snmallocshim SHARED ${SHARED_FILES})
     add_shim(snmallocshim-1mib SHARED ${SHARED_FILES})
     target_compile_definitions(snmallocshim-1mib PRIVATE IS_ADDRESS_SPACE_CONSTRAINED)
+    # Build a shim with some settings from oe.
+    add_shim(snmallocshim-oe SHARED ${SHARED_FILES})
+    oe_simulate(snmallocshim-oe)
   endif()
 
   if(SNMALLOC_RUST_SUPPORT)
@@ -260,7 +267,7 @@ if(NOT DEFINED SNMALLOC_ONLY_HEADER_LIBRARY)
   foreach(TEST_CATEGORY ${TEST_CATEGORIES})
     subdirlist(TESTS ${TESTDIR}/${TEST_CATEGORY})
     foreach(TEST ${TESTS})
-      foreach(SUPER_SLAB_SIZE 1;16)
+      foreach(SUPER_SLAB_SIZE 1;16;oe)
         unset(SRC)
         aux_source_directory(${TESTDIR}/${TEST_CATEGORY}/${TEST} SRC)
         set(TESTNAME "${TEST_CATEGORY}-${TEST}-${SUPER_SLAB_SIZE}")
@@ -269,6 +276,9 @@ if(NOT DEFINED SNMALLOC_ONLY_HEADER_LIBRARY)
         if (${SUPER_SLAB_SIZE} EQUAL 1)
           target_compile_definitions(${TESTNAME} PRIVATE IS_ADDRESS_SPACE_CONSTRAINED)
         endif()
+        if (${SUPER_SLAB_SIZE} EQUAL oe)
+          oe_simulate(${TESTNAME})
+        endif()
         target_link_libraries(${TESTNAME} snmalloc_lib)
         if (${TEST} MATCHES "release-.*")
           message(STATUS "Adding test: ${TESTNAME} only for release configs")
diff --git a/src/mem/allocconfig.h b/src/mem/allocconfig.h
index 9704b94..ae6240b 100644
--- a/src/mem/allocconfig.h
+++ b/src/mem/allocconfig.h
@@ -50,6 +50,15 @@ namespace snmalloc
 #endif
     ;
 
+  // Specifies even smaller slab and super slab sizes for open enclave.
+  static constexpr size_t REALLY_ADDRESS_SPACE_CONSTRAINED =
+#ifdef IS_REALLY_ADDRESS_SPACE_CONSTRAINED
+    true
+#else
+    false
+#endif
+    ;
+
   static constexpr size_t RESERVE_MULTIPLE =
 #ifdef USE_RESERVE_MULTIPLE
     USE_RESERVE_MULTIPLE
@@ -100,14 +109,17 @@ namespace snmalloc
   static constexpr size_t MIN_ALLOC_BITS = bits::ctz_const(MIN_ALLOC_SIZE);
 
   // Slabs are 64 KiB unless constrained to 16 KiB.
-  static constexpr size_t SLAB_BITS = ADDRESS_SPACE_CONSTRAINED ? 14 : 16;
+  static constexpr size_t SLAB_BITS = REALLY_ADDRESS_SPACE_CONSTRAINED ?
+    13 :
+    (ADDRESS_SPACE_CONSTRAINED ? 14 : 16);
   static constexpr size_t SLAB_SIZE = 1 << SLAB_BITS;
   static constexpr size_t SLAB_MASK = ~(SLAB_SIZE - 1);
 
   // Superslabs are composed of this many slabs. Slab offsets are encoded as
   // a byte, so the maximum count is 256. This must be a power of two to
   // allow fast masking to find a superslab start address.
-  static constexpr size_t SLAB_COUNT_BITS = ADDRESS_SPACE_CONSTRAINED ? 6 : 8;
+  static constexpr size_t SLAB_COUNT_BITS =
+    REALLY_ADDRESS_SPACE_CONSTRAINED ? 5 : (ADDRESS_SPACE_CONSTRAINED ? 6 : 8);
   static constexpr size_t SLAB_COUNT = 1 << SLAB_COUNT_BITS;
   static constexpr size_t SUPERSLAB_SIZE = SLAB_SIZE * SLAB_COUNT;
   static constexpr size_t SUPERSLAB_MASK = ~(SUPERSLAB_SIZE - 1);
diff --git a/src/test/func/two_alloc_types/alloc2.cc b/src/test/func/two_alloc_types/alloc2.cc
index 5338054..67be116 100644
--- a/src/test/func/two_alloc_types/alloc2.cc
+++ b/src/test/func/two_alloc_types/alloc2.cc
@@ -1,4 +1,7 @@
-#undef IS_ADDRESS_SPACE_CONSTRAINED
+// Remove parameters feed from test harness
+#undef ADDRESS_SPACE_CONSTRAINED
+#undef REALLY_ADDRESS_SPACE_CONSTRAINED
+
 #define SNMALLOC_NAME_MANGLE(a) host_##a
 #define NO_BOOTSTRAP_ALLOCATOR
 #define SNMALLOC_EXPOSE_PAGEMAP