diff --git a/Android.bp b/Android.bp
index 81b0546..2f5c631 100644
--- a/Android.bp
+++ b/Android.bp
@@ -23,8 +23,9 @@ common_cflags = [
     "-DGUARD_SIZE_DIVISOR=2",
     "-DREGION_QUARANTINE_RANDOM_SIZE=128",
     "-DREGION_QUARANTINE_QUEUE_SIZE=1024",
-    "-DREGION_QUARANTINE_SKIP_THRESHOLD=33554432",
+    "-DREGION_QUARANTINE_SKIP_THRESHOLD=33554432", // 32MiB
     "-DFREE_SLABS_QUARANTINE_RANDOM_SIZE=32",
+    "-DCONFIG_CLASS_REGION_SIZE=1073741824", // 1GiB
 ]
 
 cc_defaults {
diff --git a/Makefile b/Makefile
index 99a24d1..8ebbf11 100644
--- a/Makefile
+++ b/Makefile
@@ -12,8 +12,9 @@ CONFIG_GUARD_SLABS_INTERVAL := 1
 CONFIG_GUARD_SIZE_DIVISOR := 2
 CONFIG_REGION_QUARANTINE_RANDOM_SIZE := 128
 CONFIG_REGION_QUARANTINE_QUEUE_SIZE := 1024
-CONFIG_REGION_QUARANTINE_SKIP_THRESHOLD := 33554432
+CONFIG_REGION_QUARANTINE_SKIP_THRESHOLD := 33554432 # 32MiB
 CONFIG_FREE_SLABS_QUARANTINE_RANDOM_SIZE := 32
+CONFIG_CLASS_REGION_SIZE := 137438953472 # 128GiB
 
 define safe_flag
 $(shell $(CC) -E $1 - </dev/null >/dev/null 2>&1 && echo $1)
@@ -77,7 +78,8 @@ CPPFLAGS += \
     -DREGION_QUARANTINE_RANDOM_SIZE=$(CONFIG_REGION_QUARANTINE_RANDOM_SIZE) \
     -DREGION_QUARANTINE_QUEUE_SIZE=$(CONFIG_REGION_QUARANTINE_QUEUE_SIZE) \
     -DREGION_QUARANTINE_SKIP_THRESHOLD=$(CONFIG_REGION_QUARANTINE_SKIP_THRESHOLD) \
-    -DFREE_SLABS_QUARANTINE_RANDOM_SIZE=$(CONFIG_FREE_SLABS_QUARANTINE_RANDOM_SIZE)
+    -DFREE_SLABS_QUARANTINE_RANDOM_SIZE=$(CONFIG_FREE_SLABS_QUARANTINE_RANDOM_SIZE) \
+    -DCONFIG_CLASS_REGION_SIZE=$(CONFIG_CLASS_REGION_SIZE)
 
 libhardened_malloc.so: $(OBJECTS)
 	$(CC) $(CFLAGS) $(LDFLAGS) -shared $^ $(LDLIBS) -o $@
diff --git a/README.md b/README.md
index fd36d9a..7a38953 100644
--- a/README.md
+++ b/README.md
@@ -159,6 +159,8 @@ for the chosen values are not written yet, so use them at your own peril:
   the size threshold where large allocations will not be quarantined
 * `CONFIG_FREE_SLABS_QUARANTINE_RANDOM_SIZE`: `32` (default) to control the
   number of slots in the random array used to randomize free slab reuse
+* `CONFIG_CLASS_REGION_SIZE`: `34359738368` (default) to control the size of
+  the size class regions
 
 There will be more control over enabled features in the future along with
 control over fairly arbitrarily chosen values like the size of empty slab
diff --git a/h_malloc.c b/h_malloc.c
index d065c71..7d659af 100644
--- a/h_malloc.c
+++ b/h_malloc.c
@@ -210,7 +210,7 @@ struct __attribute__((aligned(CACHELINE_SIZE))) size_class {
     size_t metadata_count_unguarded;
 };
 
-#define CLASS_REGION_SIZE (128ULL * 1024 * 1024 * 1024)
+#define CLASS_REGION_SIZE (size_t)CONFIG_CLASS_REGION_SIZE
 #define REAL_CLASS_REGION_SIZE (CLASS_REGION_SIZE * 2)
 static const size_t slab_region_size = REAL_CLASS_REGION_SIZE * N_SIZE_CLASSES;
 static_assert(PAGE_SIZE == 4096, "bitmap handling will need adjustment for other page sizes");