--- a/mojoshader.c	Mon Jul 20 16:14:43 2020 -0400
+++ b/mojoshader.c	Mon Jul 20 18:53:54 2020 -0400
@@ -1504,6 +1504,12 @@
         fail(ctx, "RCP without replicate swizzle");
 } // state_RCP
 
+static void state_RSQ(Context *ctx)
+{
+    if (!replicate_swizzle(ctx->source_args[0].swizzle))
+        fail(ctx, "RSQ without replicate swizzle");
+} // state_RSQ
+
 static void state_LOOP(Context *ctx)
 {
     if (ctx->source_args[0].regtype != REG_TYPE_LOOP)

--- a/mojoshader_assembler.c	Mon Jul 20 16:14:43 2020 -0400
+++ b/mojoshader_assembler.c	Mon Jul 20 18:53:54 2020 -0400
@@ -1254,7 +1254,8 @@
     ctx->tokenbufpos = 0;
     ctx->default_writemask = instruction->default_writemask;
 
-    if (opcode == OPCODE_RCP)  // RCP has an implicit swizzle of .xxxx if not specified.
+    // RCP and RSQ have an implicit swizzle of .xxxx if not specified.
+    if ((opcode == OPCODE_RCP) || (opcode == OPCODE_RSQ))
         ctx->default_swizzle = 0;  // .xxxx replicate swizzle.
 
     const int tokcount = instruction->parse_args(ctx);

--- a/mojoshader_internal.h	Mon Jul 20 16:14:43 2020 -0400
+++ b/mojoshader_internal.h	Mon Jul 20 18:53:54 2020 -0400
@@ -413,6 +413,7 @@
 
 // we need to reference these by explicit value occasionally...
 #define OPCODE_RCP 6
+#define OPCODE_RSQ 7
 #define OPCODE_RET 28
 #define OPCODE_IF 40
 #define OPCODE_IFC 41
@@ -781,7 +782,7 @@
 INSTRUCTION(MAD, "MAD", 1, DSSS, MOJOSHADER_TYPE_ANY, 0xF)
 INSTRUCTION(MUL, "MUL", 1, DSS, MOJOSHADER_TYPE_ANY, 0xF)
 INSTRUCTION_STATE(RCP, "RCP", 1, DS, MOJOSHADER_TYPE_ANY, 0xF)
-INSTRUCTION(RSQ, "RSQ", 1, DS, MOJOSHADER_TYPE_ANY, 0xF)
+INSTRUCTION_STATE(RSQ, "RSQ", 1, DS, MOJOSHADER_TYPE_ANY, 0xF)
 INSTRUCTION(DP3, "DP3", 1, DSS, MOJOSHADER_TYPE_ANY, 0xF)
 INSTRUCTION_STATE(DP4, "DP4", 1, DSS, MOJOSHADER_TYPE_ANY, 0xF)
 INSTRUCTION(MIN, "MIN", 1, DSS, MOJOSHADER_TYPE_ANY, 0xF)