diff --git a/src/arena.c b/src/arena.c
index 64a731649d..323c5bdc7d 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -12,8 +12,13 @@
  */
 #define PM_ARENA_BLOCK_SIZE(data_size) (offsetof(pm_arena_block_t, data) + (data_size))
 
-/** Initial block data size: 8 KB. */
+/**
+ * Initial block data size: 8 KB. An embedder on a small heap can define a
+ * smaller one; a parse of a short program then takes blocks of that size.
+ */
+#ifndef PM_ARENA_INITIAL_SIZE
 #define PM_ARENA_INITIAL_SIZE 8192
+#endif
 
 /** Double the block size every this many blocks. */
 #define PM_ARENA_GROWTH_INTERVAL 8
diff --git a/src/errors_format.c b/src/errors_format.c
index 32956a613a..afb6ee1214 100644
--- a/src/errors_format.c
+++ b/src/errors_format.c
@@ -8,6 +8,10 @@
 #include "prism/internal/parser.h"
 
 #include <assert.h>
+// Include sys/types.h before inttypes.h to work around an issue with certain
+// versions of GCC and newlib which causes omission of the 64-bit PRI macros
+// (see 61ebe5123; the removal of defines.h dropped it).
+#include <sys/types.h>
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
diff --git a/src/integer.c b/src/integer.c
index 104052412d..deb317695a 100644
--- a/src/integer.c
+++ b/src/integer.c
@@ -4,6 +4,10 @@
 #include "prism/internal/buffer.h"
 
 #include <assert.h>
+// Include sys/types.h before inttypes.h to work around an issue with certain
+// versions of GCC and newlib which causes omission of PRIu64 and the other
+// 64-bit macros (see 61ebe5123; the removal of defines.h dropped it).
+#include <sys/types.h>
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stddef.h>
diff --git a/src/prism.c b/src/prism.c
index 5bdab809a2..01b91fee91 100644
--- a/src/prism.c
+++ b/src/prism.c
@@ -23254,6 +23254,16 @@ pm_parser_init_shebang(pm_parser_t *parser, const pm_options_t *options, const c
     parser->frozen_string_literal = next_options.frozen_string_literal;
 }
 
+/**
+ * The smallest capacity the constant pool starts with, whatever the source
+ * size suggests. An embedder that interns a fixed set of names into the pool
+ * at every parse (a symbol table) can raise it to that set's size, so the
+ * pool does not grow to hold them and leave each outgrown array in the arena.
+ */
+#ifndef PM_CONSTANT_POOL_MIN_CAPACITY
+#define PM_CONSTANT_POOL_MIN_CAPACITY 4
+#endif
+
 /**
  * Initialize a parser with the given start and end pointers.
  */
@@ -23331,7 +23341,8 @@ pm_parser_init(pm_arena_t *arena, pm_parser_t *parser, const uint8_t *source, si
      * frequency. Resizes are cheap with arena allocation, so we lean toward
      * under-estimating. */
     uint32_t constant_size = ((uint32_t) size) / 120;
-    pm_constant_pool_init(&parser->metadata_arena, &parser->constant_pool, constant_size < 4 ? 4 : constant_size);
+    if (constant_size < PM_CONSTANT_POOL_MIN_CAPACITY) constant_size = PM_CONSTANT_POOL_MIN_CAPACITY;
+    pm_constant_pool_init(&parser->metadata_arena, &parser->constant_pool, constant_size);
 
     /* Initialize the line offset list. Similar to the constant pool, we are
      * going to estimate the number of newlines that we will need based on the