diff --git a/assemble.c b/assemble.c
index 21dc177..9a76512 100644
--- a/assemble.c
+++ b/assemble.c
@@ -400,17 +400,36 @@ do_mcalled_macro:
                 case P_RADIX:
                     {
                         int             old_radix = radix;
+                        EX_TREE        *value;
+                        int             ok = 1;
 
-                        radix = strtoul(cp, &cp, 10);
-                        if (radix != 8 && radix != 10 && radix != 16 && radix != 2) {
-                            radix = old_radix;
-                            report(stack->top, "Illegal radix\n");
-                            return 0;
+                        cp = skipwhite(cp);
+                        if (EOL(*cp)) {
+                            /* If no argument, assume 8 */
+                            radix = 8;
+                            return 1;
                         }
-                        /* Sometimes a decimal point appears after the value */
-                        if (*cp == '.')
-                            cp++;
-                        return CHECK_EOL;
+                        /* Parse the argument in decimal radix */
+                        radix = 10;
+                        value = parse_expr(cp, 0);
+                        cp = value->cp;
+
+                        if (value->type != EX_LIT) {
+                            report(stack->top, "Argument to .RADIX must be constant\n");
+                            radix = old_radix;
+                            ok = 0;
+                        } else {
+                            radix = value->data.lit;
+                            list_value(stack->top, radix);
+                            if (radix != 8 && radix != 10 &&
+                                radix != 2 && radix != 16) {
+                                radix = old_radix;
+                                report(stack->top, "Argument to .RADIX must be 2, 8, 10, or 16\n");
+                                ok = 0;
+                            }
+                        }
+                        free_tree(value);
+                        return ok && CHECK_EOL;
                     }
 
                 case P_FLT4:
diff --git a/tests/RunTests b/tests/RunTests
index 4354b2b..c8b554a 100755
--- a/tests/RunTests
+++ b/tests/RunTests
@@ -30,6 +30,7 @@ TESTS="test-asciz \
     test-prec \
     test-psect \
     test-rad50 \
+    test-radix \
     test-reg \
     test-reloc \
     test-rept \
diff --git a/tests/test-radix.lst.ok b/tests/test-radix.lst.ok
new file mode 100644
index 0000000..1a5bbe4
--- /dev/null
+++ b/tests/test-radix.lst.ok
@@ -0,0 +1,38 @@
+       1                                ;;;;;
+       2                                ;
+       3                                ; Test .radix directive
+       4                                ;
+       5        000010                  	.RADIX	8
+       6 000000 000010                  	.WORD	10
+       7        000012                  	.RADIX	10
+       8 000002 000012                  	.WORD	10
+       9                                	.RADIX			;Default is 8
+      10 000004 000010                  	.WORD	10
+      11        000002                  	.RADIX	2
+      12 000006 000002                  	.WORD	10
+      13        000020                  	.RADIX	16
+      14 000010 000020                  	.WORD	10
+      15                                ; Odd but valid
+      16        000010                  	.RADIX	^O10		;Octal 10, i.e., 8
+      17 000012 000010                  	.WORD	10
+      18        000012                  	.RADIX	5+5
+      19 000014 000012                  	.WORD	10
+      20                                ; Errors
+test-radix.mac:21: ***ERROR Argument to .RADIX must be 2, 8, 10, or 16
+      21        000007                  	.RADIX	7
+      22 000016 000012                  	.WORD	10		;Radix is unchanged after error
+test-radix.mac:23: ***ERROR Argument to .RADIX must be constant
+      23                                	.RADIX	.
+      24 000020 000012                  	.WORD	10
+      24                                
+
+
+Symbol table
+
+.       000022R      001 
+
+
+Program sections:
+
+. ABS.  000000    000   (RW,I,GBL,ABS,OVR,NOSAV)
+        000022    001   (RW,I,LCL,REL,CON,NOSAV)
diff --git a/tests/test-radix.mac b/tests/test-radix.mac
new file mode 100644
index 0000000..b50e13f
--- /dev/null
+++ b/tests/test-radix.mac
@@ -0,0 +1,24 @@
+;;;;;
+;
+; Test .radix directive
+;
+	.RADIX	8
+	.WORD	10
+	.RADIX	10
+	.WORD	10
+	.RADIX			;Default is 8
+	.WORD	10
+	.RADIX	2
+	.WORD	10
+	.RADIX	16
+	.WORD	10
+; Odd but valid
+	.RADIX	^O10		;Octal 10, i.e., 8
+	.WORD	10
+	.RADIX	5+5
+	.WORD	10
+; Errors
+	.RADIX	7
+	.WORD	10		;Radix is unchanged after error
+	.RADIX	.
+	.WORD	10