diff --git a/test/ruby/test_yjit.rb b/test/ruby/test_yjit.rb
index 0905b68218..9b26e6c37f 100644
--- a/test/ruby/test_yjit.rb
+++ b/test/ruby/test_yjit.rb
@@ -3,7 +3,7 @@ require 'test/unit'
 require 'envutil'
 require 'tmpdir'
 
-return unless YJIT.enabled?
+return unless defined?(YJIT) && YJIT.enabled?
 
 # Tests for YJIT with assertions on compilation and side exits
 # insipired by the MJIT tests in test/ruby/test_jit.rb
diff --git a/yjit.c b/yjit.c
index bfe79822f0..a0ac959d4f 100644
--- a/yjit.c
+++ b/yjit.c
@@ -10,8 +10,6 @@
 #include "vm_sync.h"
 #include "yjit.h"
 
-#include "yjit_asm.c"
-
 #ifndef YJIT_CHECK_MODE
 # define YJIT_CHECK_MODE 0
 #endif
@@ -31,6 +29,11 @@
 // USE_MJIT comes from configure options
 #define JIT_ENABLED USE_MJIT
 
+// Check if we need to include YJIT in the build
+#if JIT_ENABLED && PLATFORM_SUPPORTED_P
+
+#include "yjit_asm.c"
+
 // Code block into which we write machine code
 static codeblock_t block;
 static codeblock_t *cb = NULL;
@@ -154,3 +157,31 @@ static uint32_t yjit_codepage_frozen_bytes = 0;
 #include "yjit_core.c"
 #include "yjit_iface.c"
 #include "yjit_codegen.c"
+
+#else
+// !JIT_ENABLED || !PLATFORM_SUPPORTED_P
+// In these builds, YJIT could never be turned on. Provide dummy
+// implementations for YJIT functions exposed to the rest of the code base.
+// See yjit.h.
+
+void Init_builtin_yjit(void) {}
+bool rb_yjit_enabled_p(void) { return false; }
+unsigned rb_yjit_call_threshold(void) { return UINT_MAX; }
+void rb_yjit_invalidate_all_method_lookup_assumptions(void) {};
+void rb_yjit_method_lookup_change(VALUE klass, ID mid) {};
+void rb_yjit_cme_invalidate(VALUE cme) {}
+void rb_yjit_collect_vm_usage_insn(int insn) {}
+void rb_yjit_collect_binding_alloc(void) {}
+void rb_yjit_collect_binding_set(void) {}
+bool rb_yjit_compile_iseq(const rb_iseq_t *iseq, rb_execution_context_t *ec) { return false; }
+void rb_yjit_init(struct rb_yjit_options *options) {}
+void rb_yjit_bop_redefined(VALUE klass, const rb_method_entry_t *me, enum ruby_basic_operators bop) {}
+void rb_yjit_constant_state_changed(void) {}
+void rb_yjit_iseq_mark(const struct rb_iseq_constant_body *body) {}
+void rb_yjit_iseq_update_references(const struct rb_iseq_constant_body *body) {}
+void rb_yjit_iseq_free(const struct rb_iseq_constant_body *body) {}
+void rb_yjit_before_ractor_spawn(void) {}
+void rb_yjit_constant_ic_update(const rb_iseq_t *iseq, IC ic) {}
+void rb_yjit_tracing_invalidate_all(void) {}
+
+#endif // if JIT_ENABLED && PLATFORM_SUPPORTED_P
diff --git a/yjit.rb b/yjit.rb
index 79511685d1..cbd2ea1e44 100644
--- a/yjit.rb
+++ b/yjit.rb
@@ -1,3 +1,10 @@
+# This module allows for introspection on YJIT, CRuby's experimental in-process
+# just-in-time compiler. This module is for development purposes only;
+# everything in this module is highly implementation specific and comes with no
+# API stability guarantee whatsoever.
+#
+# This module is only defined when YJIT has support for the particular platform
+# on which CRuby is built.
 module YJIT
   if defined?(Disasm)
     def self.disasm(iseq, tty: $stdout && $stdout.tty?)