diff --git a/include/mruby/boxing_word.h b/include/mruby/boxing_word.h
index 7fb88d974..4fbbd3b31 100644
--- a/include/mruby/boxing_word.h
+++ b/include/mruby/boxing_word.h
@@ -14,8 +14,37 @@
 #ifndef MRB_NO_FLOAT
 struct RFloat {
   MRB_OBJECT_HEADER;
+#ifdef MRB_WORDBOX_NO_FLOAT_TRUNCATE
+  /* avoid 8-byte alignment on 32-bit; use memcpy-based accessors */
+  char f[sizeof(mrb_float)];
+#else
   mrb_float f;
+#endif
 };
+
+#include <string.h>
+
+static inline mrb_float
+mrb_rfloat_value(const struct RFloat *p)
+{
+#ifdef MRB_WORDBOX_NO_FLOAT_TRUNCATE
+  mrb_float f;
+  memcpy(&f, p->f, sizeof(mrb_float));
+  return f;
+#else
+  return p->f;
+#endif
+}
+
+static inline void
+mrb_rfloat_set(struct RFloat *p, mrb_float f)
+{
+#ifdef MRB_WORDBOX_NO_FLOAT_TRUNCATE
+  memcpy(p->f, &f, sizeof(mrb_float));
+#else
+  p->f = f;
+#endif
+}
 #endif
 
 struct RInteger {
@@ -155,7 +184,7 @@ MRB_API mrb_value mrb_boxing_int_value(struct mrb_state*, mrb_int);
 MRB_API mrb_float mrb_word_boxing_value_float(mrb_value v);
 #define mrb_float(o) mrb_word_boxing_value_float(o)
 #else
-#define mrb_float(o) mrb_val_union(o).fp->f
+#define mrb_float(o) mrb_rfloat_value(mrb_val_union(o).fp)
 #endif
 #endif
 #define mrb_fixnum(o)  (mrb_int)(((intptr_t)(o).w) >> WORDBOX_FIXNUM_SHIFT)
diff --git a/src/class.c b/src/class.c
index 04eeb562d..1f95a08d6 100644
--- a/src/class.c
+++ b/src/class.c
@@ -3997,7 +3997,7 @@ init_copy(mrb_state *mrb, mrb_value dest, mrb_value obj)
     case MRB_TT_FLOAT:
       {
         struct RFloat *f = (struct RFloat*)mrb_obj_ptr(dest);
-        f->f = mrb_float(obj);
+        mrb_rfloat_set(f, mrb_float(obj));
       }
       break;
 #endif
diff --git a/src/etc.c b/src/etc.c
index d45bbeee5..c35bf262c 100644
--- a/src/etc.c
+++ b/src/etc.c
@@ -288,7 +288,7 @@ mrb_word_boxing_float_value(mrb_state *mrb, mrb_float f)
 
 #ifdef MRB_WORDBOX_NO_FLOAT_TRUNCATE
   v.p = mrb_obj_alloc(mrb, MRB_TT_FLOAT, mrb->float_class);
-  v.fp->f = f;
+  mrb_rfloat_set(v.fp, f);
   v.bp->frozen = 1;
 #elif defined(MRB_64BIT) && defined(MRB_USE_FLOAT32)
   v.w = 0;
@@ -323,7 +323,7 @@ mrb_word_boxing_float_value(mrb_state *mrb, mrb_float f)
     else {
     float_heap:
       v.p = mrb_obj_alloc(mrb, MRB_TT_FLOAT, mrb->float_class);
-      v.fp->f = f;
+      mrb_rfloat_set(v.fp, f);
       v.bp->frozen = 1;
     }
   }
@@ -357,7 +357,7 @@ mrb_word_boxing_float_value(mrb_state *mrb, mrb_float f)
     else {
     float_heap:
       v.p = mrb_obj_alloc(mrb, MRB_TT_FLOAT, mrb->float_class);
-      v.fp->f = f;
+      mrb_rfloat_set(v.fp, f);
       v.bp->frozen = 1;
     }
   }
@@ -399,7 +399,7 @@ mrb_word_boxing_value_float(mrb_value v)
   else {
     union mrb_value_ u;
     u.value = v;
-    return u.fp->f;
+    return mrb_rfloat_value(u.fp);
   }
 #else
   /* 32-bit + float32: rotation decoding */
@@ -420,7 +420,7 @@ mrb_word_boxing_value_float(mrb_value v)
   else {
     union mrb_value_ u;
     u.value = v;
-    return u.fp->f;
+    return mrb_rfloat_value(u.fp);
   }
 #endif
 }