diff --git a/ext/json/ext/fbuffer/fbuffer.h b/ext/json/ext/fbuffer/fbuffer.h
index 3f95f1f76..2616c03bd 100644
--- a/ext/json/ext/fbuffer/fbuffer.h
+++ b/ext/json/ext/fbuffer/fbuffer.h
@@ -33,7 +33,7 @@ typedef struct FBufferStruct {
 static void fbuffer_free(FBuffer *fb);
 static void fbuffer_clear(FBuffer *fb);
 static void fbuffer_append(FBuffer *fb, const char *newstr, size_t len);
-static void fbuffer_append_long(FBuffer *fb, long number);
+static void fbuffer_append_len(FBuffer *fb, rb_len_t number);
 static inline void fbuffer_append_char(FBuffer *fb, char newchr);
 static VALUE fbuffer_finalize(FBuffer *fb);
 
@@ -218,7 +218,7 @@ static inline void fbuffer_advance_to(FBuffer *fb, char *end)
 /*
  * Appends the decimal string representation of \a number into the buffer.
  */
-static void fbuffer_append_long(FBuffer *fb, long number)
+static void fbuffer_append_len(FBuffer *fb, rb_len_t number)
 {
     /*
      * The jeaiii_ultoa() function produces digits left-to-right,
@@ -231,9 +231,9 @@ static void fbuffer_append_long(FBuffer *fb, long number)
      * generated is therefore 20 (including a potential sign character).
      */
 
-    static const int MAX_CHARS_FOR_LONG = 20;
+    static const int MAX_CHARS_FOR_LEN = 20;
 
-    fbuffer_inc_capa(fb, MAX_CHARS_FOR_LONG);
+    fbuffer_inc_capa(fb, MAX_CHARS_FOR_LEN);
 
     if (number < 0) {
         fbuffer_append_reserved_char(fb, '-');
diff --git a/ext/json/ext/generator/generator.c b/ext/json/ext/generator/generator.c
index 87da10027..bc2e73726 100644
--- a/ext/json/ext/generator/generator.c
+++ b/ext/json/ext/generator/generator.c
@@ -59,7 +59,12 @@ struct generate_json_data {
     long depth;
 };
 
+#if defined(HAVE_SIMD) && defined(HAVE_SIMD_SSE2)
 static SIMD_Implementation simd_impl;
+# define init_simd_impl() (simd_impl = find_simd_implementation())
+#else
+# define init_simd_impl() (void)0
+#endif
 
 static VALUE cState_from_state_s(VALUE self, VALUE opts);
 static VALUE cState_partial_generate(VALUE self, VALUE obj, generator_func, VALUE io);
@@ -1161,7 +1166,7 @@ static void generate_json_fixnum(FBuffer *buffer, struct generate_json_data *dat
         generate_json_rfc8785_number(buffer, obj);
         return;
     }
-    fbuffer_append_long(buffer, FIX2LONG(obj));
+    fbuffer_append_len(buffer, FIX2LEN(obj));
 }
 
 static void generate_json_bignum(FBuffer *buffer, struct generate_json_data *data, VALUE obj)
@@ -2171,5 +2176,5 @@ void Init_generator(void)
 
     rb_require("json/ext/generator/state");
 
-    simd_impl = find_simd_implementation();
+    init_simd_impl();
 }
diff --git a/ext/json/ext/json.h b/ext/json/ext/json.h
index a402182d0..ba2ac2b75 100644
--- a/ext/json/ext/json.h
+++ b/ext/json/ext/json.h
@@ -7,7 +7,14 @@
 
 #ifndef HAVE_RB_LEN_T
 typedef long rb_len_t;
+#endif
+#ifndef FIX2LEN
+# define FIX2LEN FIX2LONG
+#endif
+#ifndef LEN2NUM
 # define LEN2NUM LONG2NUM
+#endif
+#ifndef PRIdLEN
 # define PRIdLEN "ld"
 #endif