diff --git a/src/cmd/compile/internal/walk/walk.go b/src/cmd/compile/internal/walk/walk.go
index d889786c728..1f0b7772634 100644
--- a/src/cmd/compile/internal/walk/walk.go
+++ b/src/cmd/compile/internal/walk/walk.go
@@ -14,6 +14,7 @@ import (
 	"cmd/compile/internal/ssagen"
 	"cmd/compile/internal/typecheck"
 	"cmd/compile/internal/types"
+	"cmd/internal/objabi"
 	"cmd/internal/src"
 )
 
@@ -203,6 +204,13 @@ func mapfast(t *types.Type) int {
 	}
 	switch reflectdata.AlgType(t.Key()) {
 	case types.AMEM32:
+		if objabi.Experiment.RegabiArgs && t.Key().NumComponents(types.CountBlankFields) != 1 {
+			// If key has multiple components, under register ABI it will
+			// be passed differently than uint32.
+			// TODO: maybe unsafe-case to uint32. But needs to make the type
+			// checker happy.
+			return mapslow
+		}
 		if !t.Key().HasPointers() {
 			return mapfast32
 		}
@@ -211,6 +219,10 @@ func mapfast(t *types.Type) int {
 		}
 		base.Fatalf("small pointer %v", t.Key())
 	case types.AMEM64:
+		if objabi.Experiment.RegabiArgs && t.Key().NumComponents(types.CountBlankFields) != 1 {
+			// See above.
+			return mapslow
+		}
 		if !t.Key().HasPointers() {
 			return mapfast64
 		}