diff --git a/gas/ChangeLog b/gas/ChangeLog
index 91af84b826d..637fc65648d 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,8 @@
+2018-09-20  Maciej W. Rozycki  <macro@linux-mips.org>
+
+	* config/tc-s12z.c (lex_opr): Use an auxiliary unsigned variable
+	in encoding a constant operand.
+
 2018-09-20  Maciej W. Rozycki  <macro@linux-mips.org>
 
 	* config/tc-ppc.c (ppc_dwsect): Use `valueT' rather than
diff --git a/gas/config/tc-s12z.c b/gas/config/tc-s12z.c
index 736f062b80e..d3b2ea4c4af 100644
--- a/gas/config/tc-s12z.c
+++ b/gas/config/tc-s12z.c
@@ -614,31 +614,33 @@ lex_opr (uint8_t *buffer, int *n_bytes, expressionS *exp)
       buffer[3] = 0;
       if (exp->X_op == O_constant)
 	{
-	  if (exp->X_add_number < (0x1U << 14))
+	  valueT value = exp->X_add_number;
+
+	  if (value < (0x1U << 14))
 	    {
 	      *xb = 0x00;
 	      *n_bytes = 2;
-	      *xb |= exp->X_add_number >> 8;
-	      buffer[1] = exp->X_add_number;
+	      *xb |= value >> 8;
+	      buffer[1] = value;
 	    }
-	  else if (exp->X_add_number < (0x1U << 19))
+	  else if (value < (0x1U << 19))
 	    {
 	      *xb = 0xf8;
-	      if (exp->X_add_number & (0x1U << 17))
+	      if (value & (0x1U << 17))
 		*xb |= 0x04;
-	      if (exp->X_add_number & (0x1U << 16))
+	      if (value & (0x1U << 16))
 		*xb |= 0x01;
 	      *n_bytes = 3;
-	      buffer[1] = exp->X_add_number >> 8;
-	      buffer[2] = exp->X_add_number;
+	      buffer[1] = value >> 8;
+	      buffer[2] = value;
 	    }
 	  else
 	    {
 	      *xb = 0xfa;
 	      *n_bytes = 4;
-	      buffer[1] = exp->X_add_number >> 16;
-	      buffer[2] = exp->X_add_number >> 8;
-	      buffer[3] = exp->X_add_number;
+	      buffer[1] = value >> 16;
+	      buffer[2] = value >> 8;
+	      buffer[3] = value;
 	    }
 	}
       return 1;