diff --git a/opcodes/ChangeLog b/opcodes/ChangeLog
index 0c6994e90d..a6000cebbc 100644
--- a/opcodes/ChangeLog
+++ b/opcodes/ChangeLog
@@ -1,3 +1,9 @@
+2018-05-08  Alan Modra  <amodra@gmail.com>
+
+	* ppc-dis.c (PPC_OPCD_SEGS): Define using PPC_OP.
+	(VLE_OPCD_SEGS, SPE2_OPCD_SEGS): Similarly, using macros used to
+	partition opcode space for index lookup.
+
 2018-05-07  Peter Bergner  <bergner@vnet.ibm.com.com>
 
 	* ppc-dis.c (print_insn_powerpc) <insn_is_short>: Replace this...
diff --git a/opcodes/ppc-dis.c b/opcodes/ppc-dis.c
index 0f7d7bacfb..412aae000d 100644
--- a/opcodes/ppc-dis.c
+++ b/opcodes/ppc-dis.c
@@ -367,12 +367,12 @@ powerpc_init_dialect (struct disassemble_info *info)
   POWERPC_DIALECT(info) = dialect;
 }
 
-#define PPC_OPCD_SEGS 64
-static unsigned short powerpc_opcd_indices[PPC_OPCD_SEGS+1];
-#define VLE_OPCD_SEGS 32
-static unsigned short vle_opcd_indices[VLE_OPCD_SEGS+1];
-#define SPE2_OPCD_SEGS 13
-static unsigned short spe2_opcd_indices[SPE2_OPCD_SEGS+1];
+#define PPC_OPCD_SEGS (1 + PPC_OP (-1))
+static unsigned short powerpc_opcd_indices[PPC_OPCD_SEGS + 1];
+#define VLE_OPCD_SEGS (1 + VLE_OP_TO_SEG (VLE_OP (-1, 0xffff)))
+static unsigned short vle_opcd_indices[VLE_OPCD_SEGS + 1];
+#define SPE2_OPCD_SEGS (1 + SPE2_XOP_TO_SEG (SPE2_XOP (-1)))
+static unsigned short spe2_opcd_indices[SPE2_OPCD_SEGS + 1];
 
 /* Calculate opcode table indices to speed up disassembly,
    and init dialect.  */