diff --git a/src/debug.h b/src/debug.h
index f961d6e..babbaea 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -14,14 +14,14 @@
 #define __debug_print_h
 
 #define DEBUG_ALLOC 1
-#define DEBUG_STACK 2
-#define DEBUG_ARITH 4
-#define DEBUG_EVAL 8
-#define DEBUG_LAMBDA 16
-#define DEBUG_BOOTSTRAP 32
-#define DEBUG_IO 64
+#define DEBUG_ARITH 2
+#define DEBUG_BIND 4
+#define DEBUG_BOOTSTRAP 8
+#define DEBUG_EVAL 16
+#define DEBUG_IO 32
+#define DEBUG_LAMBDA 64
 #define DEBUG_REPL 128
-#define DEBUG_BIND 256
+#define DEBUG_STACK 256
 
 extern int verbosity;
 
diff --git a/src/memory/dump.c b/src/memory/dump.c
index a5faa87..fc9175d 100644
--- a/src/memory/dump.c
+++ b/src/memory/dump.c
@@ -84,7 +84,7 @@ void dump_object( FILE * output, struct cons_pointer pointer ) {
                       L"\t\tInteger cell: value %ld, count %u\n",
                       cell.payload.integer.value, cell.count );
             if ( !nilp( cell.payload.integer.more ) ) {
-                fputws( L"\t\tBIGNUM! More at\n:", output );
+                fputws( L"\t\tBIGNUM! More at:\n", output );
                 dump_object( output, cell.payload.integer.more );
             }
             break;
diff --git a/unit-tests/bignum-add.sh b/unit-tests/bignum-add.sh
new file mode 100644
index 0000000..678b766
--- /dev/null
+++ b/unit-tests/bignum-add.sh
@@ -0,0 +1,155 @@
+#!/bin/bash
+
+#####################################################################
+# add two large numbers, not actally bignums to produce a smallnum
+# (right on the boundary)
+a=1152921504606846975
+b=1
+expected='1152921504606846976'
+output=`echo "(+ $a $b)" | target/psse -v 2 2>psse.log`
+
+actual=`echo $output |\
+  tail -1 |\
+  sed 's/\,//g'`
+
+echo -n "adding $a to $b: "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+echo -n "checking no bignum was created: "
+grep -v 'BIGNUM!' psse.log > /dev/null
+if [ $? -eq "0" ]
+then
+    echo "OK"
+else
+    echo "Fail"
+    exit 1
+fi
+
+#####################################################################
+# add two numbers, not actally bignums to produce a bignum
+# (just over the boundary)
+a='1152921504606846976'
+b=1
+expected='1152921504606846977'
+output=`echo "(+ $a $b)" | target/psse -v 2 2>psse.log`
+
+actual=`echo $output |\
+  tail -1 |\
+  sed 's/\,//g'`
+
+echo -n "adding $a to $b: "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+echo -n "checking a bignum was created: "
+grep 'BIGNUM!' psse.log > /dev/null
+if [ $? -eq "0" ]
+then
+    echo "OK"
+else
+    echo "Fail"
+    exit 1
+fi
+
+#####################################################################
+# add a bignum and a smallnum to produce a bignum
+# (just over the boundary)
+a='1152921504606846977'
+b=1
+expected='1152921504606846978'
+output=`echo "(+ $a $b)" | target/psse -v 2 2>psse.log`
+
+actual=`echo $output |\
+  tail -1 |\
+  sed 's/\,//g'`
+
+echo -n "adding $a to $b: "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+echo -n "checking a bignum was created: "
+grep 'BIGNUM!' psse.log > /dev/null
+if [ $? -eq "0" ]
+then
+    echo "OK"
+else
+    echo "Fail"
+    exit 1
+fi
+
+#####################################################################
+# add a smallnum and a bignum to produce a bignum
+# (just over the boundary)
+a=1
+b=1152921504606846977
+expected='1152921504606846978'
+output=`echo "(+ $a $b)" | target/psse -v 2 2>psse.log`
+
+actual=`echo $output |\
+  tail -1 |\
+  sed 's/\,//g'`
+
+echo -n "adding $a to $b: "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+echo -n "checking a bignum was created: "
+grep 'BIGNUM!' psse.log > /dev/null
+if [ $? -eq "0" ]
+then
+    echo "OK"
+else
+    echo "Fail"
+    exit 1
+fi
+
+#####################################################################
+# add two bignums to produce a bignum
+a=10000000000000000000
+b=10000000000000000000
+expected='20000000000000000000'
+output=`echo "(+ $a $b)" | target/psse -v 2 2>psse.log`
+
+actual=`echo $output |\
+  tail -1 |\
+  sed 's/\,//g'`
+
+echo -n "adding $a to $b: "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+echo -n "checking a bignum was created: "
+grep 'BIGNUM!' psse.log > /dev/null
+if [ $? -eq "0" ]
+then
+    echo "OK"
+else
+    echo "Fail"
+    exit 1
+fi
diff --git a/unit-tests/bignum-expt.sh b/unit-tests/bignum-expt.sh
new file mode 100644
index 0000000..ab9cb24
--- /dev/null
+++ b/unit-tests/bignum-expt.sh
@@ -0,0 +1,135 @@
+#!/bin/bash
+
+#####################################################################
+# last 'smallnum' value:
+# sbcl calculates (expt 2 59) => 576460752303423488
+expected='576460752303423488'
+
+output=`target/psse <<EOF
+(progn
+  (set! expt (lambda
+              (n x)
+              (cond
+                ((= x 1) n)
+                (t (* n (expt n (- x 1)))))))
+  nil)
+  (expt 2 59)
+EOF`
+
+actual=`echo "$output" | tail -1 | sed 's/\,//g'`
+
+echo -n "(expt 2 59): "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+#####################################################################
+# first 'bignum' value (right on the boundary):
+# sbcl calculates (expt 2 60) => 1152921504606846976
+expected='1152921504606846976'
+
+output=`target/psse <<EOF
+(progn
+  (set! expt (lambda
+              (n x)
+              (cond
+                ((= x 1) n)
+                (t (* n (expt n (- x 1)))))))
+  nil)
+  (expt 2 60)
+EOF`
+
+actual=`echo "$output" | tail -1 | sed 's/\,//g'`
+
+echo -n "(expt 2 60): "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+#####################################################################
+# second 'bignum' value (definitely a bignum):
+# sbcl calculates (expt 2 61) => 2305843009213693952
+expected='2305843009213693952'
+
+output=`target/psse <<EOF
+(progn
+  (set! expt (lambda
+              (n x)
+              (cond
+                ((= x 1) n)
+                (t (* n (expt n (- x 1)))))))
+  nil)
+  (expt 2 61)
+EOF`
+
+actual=`echo "$output" | tail -1 | sed 's/\,//g'`
+
+echo -n "(expt 2 61): "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+
+
+# sbcl calculates (expt 2 64) => 18446744073709551616
+expected='18446744073709551616'
+
+output=`target/psse <<EOF
+(progn
+  (set! expt (lambda
+              (n x)
+              (cond
+                ((= x 1) n)
+                (t (* n (expt n (- x 1)))))))
+  nil)
+  (expt 2 64)
+EOF`
+
+actual=`echo "$output" | tail -1 | sed 's/\,//g'`
+
+echo -n "(expt 2 64): "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+# sbcl calculates (expt 2 65) => 36893488147419103232
+expected='36893488147419103232'
+
+output=`target/psse <<EOF
+(progn
+  (set! expt (lambda
+              (n x)
+              (cond
+                ((= x 1) n)
+                (t (* n (expt n (- x 1)))))))
+  nil)
+  (expt 2 65)
+EOF`
+
+actual=`echo "$output" | tail -1 | sed 's/\,//g'`
+
+echo -n "(expt 2 65): "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+exit 0
diff --git a/unit-tests/bignum-print.sh b/unit-tests/bignum-print.sh
new file mode 100644
index 0000000..c030f37
--- /dev/null
+++ b/unit-tests/bignum-print.sh
@@ -0,0 +1,57 @@
+#!/bin/bash
+
+#####################################################################
+# large number, not actally a bignum
+expected='576460752303423488'
+output=`echo "(progn (print $expected) nil)" | target/psse`
+
+actual=`echo $output |\
+  sed 's/\,//g' |\
+  sed 's/[^0-9]*\([0-9]*\).*/\1/'`
+
+echo -n "printing $expected: "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+#####################################################################
+# right on the boundary
+expected='1152921504606846976'
+output=`echo "(progn (print $expected) nil)" | target/psse`
+
+actual=`echo $output |\
+  sed 's/\,//g' |\
+  sed 's/[^0-9]*\([0-9]*\).*/\1/'`
+
+echo -n "printing $expected: "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+#####################################################################
+# definitely a bignum
+expected='2305843009213693952'
+output=`echo "(progn (print $expected) nil)" | target/psse`
+
+actual=`echo $output |\
+  sed 's/\,//g' |\
+  sed 's/[^0-9]*\([0-9]*\).*/\1/'`
+
+echo -n "printing $expected: "
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi
+
+exit 0