diff --git a/Core/MIPS/IR/IRCompFPU.cpp b/Core/MIPS/IR/IRCompFPU.cpp
index b0edeea0cf..3c3ed87d03 100644
--- a/Core/MIPS/IR/IRCompFPU.cpp
+++ b/Core/MIPS/IR/IRCompFPU.cpp
@@ -226,7 +226,8 @@ void IRFrontend::Comp_mxc1(MIPSOpcode op) {
 			UpdateRoundingMode();
 			ApplyRoundingMode();
 		} else {
-			Comp_Generic(op);
+			// Maybe not strictly invalid?  But likely invalid.
+			INVALIDOP;
 		}
 		return;
 	default:
diff --git a/Core/MIPS/IR/IRCompVFPU.cpp b/Core/MIPS/IR/IRCompVFPU.cpp
index c902951d96..c80fa6e1ff 100644
--- a/Core/MIPS/IR/IRCompVFPU.cpp
+++ b/Core/MIPS/IR/IRCompVFPU.cpp
@@ -782,6 +782,10 @@ namespace MIPSComp {
 		if (optype == 0) {
 			if (js.HasUnknownPrefix() || !IsPrefixWithinSize(js.prefixS, op))
 				DISABLE;
+		} else if (optype == 1 || optype == 2) {
+			// D prefix is fine for these, and used sometimes.
+			if (js.HasUnknownPrefix() || js.HasSPrefix())
+				DISABLE;
 		} else {
 			// Many of these apply the D prefix strangely or override parts of the S prefix.
 			if (!js.HasNoPrefix())