diff --git a/compiler/src/dmd/backend/arm/instr.d b/compiler/src/dmd/backend/arm/instr.d
index e8f5cfc79e4..f40420fce9d 100644
--- a/compiler/src/dmd/backend/arm/instr.d
+++ b/compiler/src/dmd/backend/arm/instr.d
@@ -868,9 +868,19 @@ struct INSTR
                 Rt;
     }
 
-    /* Load/store register pair (unprivileged)
-     * Load/store register pair (immediate pre-indexed)
-     * Atomic memory operation
+    /* STR <Vt>,[<Xn|SP>],#<simm>  Post-index  https://www.scs.stanford.edu/~zyedidia/arm64/str_imm_fpsimd.html
+     */
+
+    /* Load/store register (unprivileged)
+     */
+
+    /* Load/store register (immediate pre-indexed)
+     */
+
+    /* STR <Vt>,[<Xn|SP>,#<simm>]! Pre-index https://www.scs.stanford.edu/~zyedidia/arm64/str_imm_fpsimd.html
+     */
+
+    /* Atomic memory operation
      */
 
     /* Load/store register (register offset)
@@ -897,8 +907,10 @@ struct INSTR
     /* Load/store register (unsigned immediate)
      * https://www.scs.stanford.edu/~zyedidia/arm64/encodingindex.html#ldst_pos
      */
-    static uint ldst_pos(uint size, uint VR, uint opc, uint imm12, ubyte Rn, ubyte Rt)
+    static uint ldst_pos(uint size, uint VR, uint opc, uint imm12, reg_t Rn, reg_t Vt)
     {
+        assert(Vt > 31);
+        reg_t Rt = Vt & 31;
         return (size  << 30) |
                (7     << 27) |
                (VR    << 26) |
@@ -909,6 +921,11 @@ struct INSTR
                 Rt;
     }
 
+    /* https://www.scs.stanford.edu/~zyedidia/arm64/str_imm_fpsimd.html
+     * STR <Vt>,[<Xn|SP>,#<simm>]  Unsigned offset
+     */
+    static uint str_imm_fpsimd(uint size, uint opc, uint imm12, reg_t Rn, reg_t Vt) { return ldst_pos(size,1,opc,imm12,Rn,Vt); }
+
     /* } */
 
     /* { ************************** Data Processing -- Register **********************************/
diff --git a/compiler/src/dmd/backend/codebuilder.d b/compiler/src/dmd/backend/codebuilder.d
index 93f9d16b33f..f668ac00981 100644
--- a/compiler/src/dmd/backend/codebuilder.d
+++ b/compiler/src/dmd/backend/codebuilder.d
@@ -35,7 +35,7 @@ struct CodeBuilder
     code** pTail;
 
     enum BADINS = 0x1234_5678;
-//    enum BADINS = 0xF940_03A8;
+//    enum BADINS = 0xF900_0FA0;
 
   nothrow:
   public:
diff --git a/compiler/src/dmd/backend/x86/cod3.d b/compiler/src/dmd/backend/x86/cod3.d
index d51c6e6fa75..ef67fdbdef2 100644
--- a/compiler/src/dmd/backend/x86/cod3.d
+++ b/compiler/src/dmd/backend/x86/cod3.d
@@ -1142,7 +1142,7 @@ static if (NTEXCEPTIONS)
         case BC.retexp:
             reg_t reg1, reg2;
             retregs = allocretregs(cgstate, e.Ety, e.ET, funcsym_p.ty(), reg1, reg2);
-	    //printf("reg1: %d, reg2: %d\n", reg1, reg2);
+            //printf("reg1: %d, reg2: %d\n", reg1, reg2);
             //printf("allocretregs returns %llx %s\n", retregs, regm_str(retregs));
 
             reg_t lreg = NOREG;
@@ -4196,6 +4196,8 @@ void prolog_gen_win64_varargs(ref CodeBuilder cdb)
 }
 
 /************************************
+ * Take the parameters passed in registers, and put them into the function's local
+ * symbol table.
  * Params:
  *      cdb = generated code sink
  *      tf = what's the type of the function
@@ -4297,8 +4299,12 @@ void prolog_loadparams(ref CodeBuilder cdb, tym_t tyf, bool pushalloc)
                 {
                     if (AArch64)
                     {
-                        // STR preg,bp,#offset
-                        cdb.gen1(INSTR.str_imm_gen(sz > 4, preg, 29, offset + localsize + 16));
+                        if (tyfloating(t.Tty))
+                            // STR preg,[bp,#offset]
+                            cdb.gen1(INSTR.str_imm_fpsimd(2 + (sz == 8),0,cast(uint)(offset + localsize + 16) >> 3,29,preg));
+                        else
+                            // STR preg,bp,#offset
+                            cdb.gen1(INSTR.str_imm_gen(sz > 4, preg, 29, offset + localsize + 16));
                     }
                     else
                     {
@@ -4448,7 +4454,7 @@ void prolog_loadparams(ref CodeBuilder cdb, tym_t tyf, bool pushalloc)
         }
     }
 
-    /* For parameters that were passed on the stack, but are enregistered,
+    /* For parameters that were passed on the stack, but are enregistered by the function,
      * initialize the registers with the parameter stack values.
      * Do not use assignaddr(), as it will replace the stack reference with
      * the register.