diff --git a/src/devices/cpu/hmcs40/hmcs40d.cpp b/src/devices/cpu/hmcs40/hmcs40d.cpp
index 0b05d8b3f76..fb59cbd5b73 100644
--- a/src/devices/cpu/hmcs40/hmcs40d.cpp
+++ b/src/devices/cpu/hmcs40/hmcs40d.cpp
@@ -81,6 +81,7 @@ static const u32 s_flags[] =
 	0
 };
 
+#ifdef COMPUTE_NEXT_PC
 // next program counter in sequence (relative)
 static const s8 s_next_pc[0x40] =
 {
@@ -89,6 +90,7 @@ static const s8 s_next_pc[0x40] =
 	-32, -31, -30, -29, -28, -27, -26, -25, -24, -23, -22, -21, -20, -19, -18, -17,
 	-15, -14, -13, -12, -11, -10, -9, -8, -7, -6, -5, -4, -3, -2, -1, -1
 };
+#endif
 
 
 static const u8 hmcs40_mnemonic[0x400] =
@@ -226,6 +228,11 @@ CPU_DISASSEMBLE(hmcs40)
 		}
 	}
 
+#ifdef COMPUTE_NEXT_PC
+	// falsifying instruction lengths like this breaks the MAME disassembler quite badly
 	int pos = s_next_pc[pc & 0x3f] & DASMFLAG_LENGTHMASK;
 	return pos | s_flags[instr] | DASMFLAG_SUPPORTED;
+#else
+	return 1 | s_flags[instr] | DASMFLAG_SUPPORTED;
+#endif
 }