diff --git a/gnovm/pkg/gnolang/op_expressions.go b/gnovm/pkg/gnolang/op_expressions.go
index 9d16941eefc..f35de3ded91 100644
--- a/gnovm/pkg/gnolang/op_expressions.go
+++ b/gnovm/pkg/gnolang/op_expressions.go
@@ -791,8 +791,7 @@ func (m *Machine) doOpConvert() {
 		} else if t.Kind() == StringKind {
 			// runes ([]int32) → string
 			if st, ok := baseOf(xv.T).(*SliceType); ok && st.Elt.Kind() == Int32Kind {
-				sv := xv.V.(*SliceValue)
-				m.incrCPU(OpCPUSlopeConvertRunesStr * int64(sv.GetLength()))
+				m.incrCPU(OpCPUSlopeConvertRunesStr * int64(xv.GetLength()))
 			}
 		}
 	}
diff --git a/gnovm/tests/files/issue_5776.gno b/gnovm/tests/files/issue_5776.gno
new file mode 100644
index 00000000000..dcb95e0b46a
--- /dev/null
+++ b/gnovm/tests/files/issue_5776.gno
@@ -0,0 +1,18 @@
+// Test case where a slice of a user-defined byte type (not uint8 or byte) is
+// converted to a string.  Same for slice of runes.
+
+package main
+
+type MyByte byte
+
+type MyRune rune
+
+func main() {
+	var y []MyByte
+	_ = string(y)
+
+	var z []MyRune
+	_ = string(z)
+}
+
+// Output: