diff --git a/basic.js b/basic.js
index 0caf0c3..0debd3c 100644
--- a/basic.js
+++ b/basic.js
@@ -523,13 +523,16 @@ this.basic = (function() {
       },
 
       'on_goto': function ON_GOTO(index /* , ...lines */) {
-        index = (index - 1) >> 0;
-        var lines = Array.prototype.slice.call(arguments, 1);
-
-        if (index < 0 || index >= lines.length) {
+        index = Math.floor(index)
+        if (index < 0 || index > 255) {
           runtime_error(ERRORS.ILLEGAL_QUANTITY);
         }
-        throw new GoToLine(lines[index]);
+        --index;
+        var lines = Array.prototype.slice.call(arguments, 1);
+
+        if (index >= 0 && index < lines.length) {
+          throw new GoToLine(lines[index]);
+        }
       },
 
       'gosub': function GOSUB(line) {
@@ -541,16 +544,19 @@ this.basic = (function() {
       },
 
       'on_gosub': function ON_GOSUB(index /* , ...lines */) {
-        index = (index - 1) >> 0;
-        var lines = Array.prototype.slice.call(arguments, 1);
-        if (index < 0 || index >= lines.length) {
+        index = Math.floor(index)
+        if (index < 0 || index > 255) {
           runtime_error(ERRORS.ILLEGAL_QUANTITY);
         }
-        state.stack.push({
-          gosub_return: state.stmt_index,
-          line_number: state.line_number
-        });
-        throw new GoToLine(lines[index]);
+        --index;
+        var lines = Array.prototype.slice.call(arguments, 1);
+        if (index >= 0 && index < lines.length) {
+          state.stack.push({
+            gosub_return: state.stmt_index,
+            line_number: state.line_number
+          });
+          throw new GoToLine(lines[index]);
+        }
       },
 
       'return': function RETURN() {
diff --git a/samples/sample.unittests.txt b/samples/sample.unittests.txt
index 73e9804..506d9c8 100644
--- a/samples/sample.unittests.txt
+++ b/samples/sample.unittests.txt
@@ -69,57 +69,102 @@
 2031 T = T + 1
 2032 T = T + 1
 2033 T = T + 1
-2039 S = (T=3) : GOSUB 1
+2034 S = (T=3) : GOSUB 1
+2035 T$ = "ON GOTO (EDGE CASE: 0)" : T = 1 : ONERR GOTO 2039
+2036 ON 0 GOTO 2037, 2038 : T = T + 3
+2037 T = T + 1
+2038 T = T + 1
+2039 S = (T=6) : POKE 216,0 : GOSUB 1
+2040 T$ = "ON GOTO (EDGE CASE: -0.1)" : T = 1 : ONERR GOTO 2044
+2041 ON -0.1 GOTO 2042, 2043 : T = T + 3
+2042 T = T + 1
+2043 T = T + 1
+2044 S = (T=1) AND (PEEK(222)=53): POKE 216,0 : GOSUB 1
 
-2040 T$ = "ON GOSUB" : T = 1 : ON 2 GOSUB 2041, 2042, 2043 : GOTO 2049
-2041 T = T + 1 : RETURN
-2042 T = T + 2 : RETURN
-2043 T = T + 3 : RETURN
-2049 S = (T=3) : GOSUB 1
 
-2050 T$ = "POP" : T = 1 : GOSUB 2055 : T = T + 1 : GOTO 2059
-2055 T = T + 1 : GOSUB 2056 : T = T + 5
-2056 POP : T = T + 1 : RETURN
-2059 S = (T=4) : GOSUB 1
+2045 T$ = "ON GOTO (EDGE CASE: 255.2)" : T = 1 : ONERR GOTO 2049
+2046 ON 255.2 GOTO 2047, 2048 : T = T + 3
+2047 T = T + 1
+2048 T = T + 1
+2049 S = (T=6) : POKE 216,0 : GOSUB 1
+2050 T$ = "ON GOTO (EDGE CASE: 256)" : T = 1 : ONERR GOTO 2054
+2051 ON -0.1 GOTO 2052, 2053 : T = T + 3
+2052 T = T + 1
+2053 T = T + 1
+2054 S = (T=1) AND (PEEK(222)=53): POKE 216,0 : GOSUB 1
 
-2060 T$ = "FOR"
+
+2060 T$ = "ON GOSUB" : T = 1 : ON 2 GOSUB 2061, 2062, 2063 : GOTO 2064
+2061 T = T + 1 : RETURN
+2062 T = T + 2 : RETURN
+2063 T = T + 3 : RETURN
+2064 S = (T=3) : GOSUB 1
+2065 T$ = "ON GOSUB (EDGE CASE: 0)" : T = 1 : ONERR GOTO 2069
+2066 ON 0 GOSUB 2067, 2068 : GOTO 2070
+2067 T = T + 2 : RETURN
+2068 T = T + 3 : RETURN
+2069 T = 255
+2070 S = (T=1) :  POKE 216,0 : GOSUB 1
+2071 T$ = "ON GOSUB (EDGE CASE: -0.1)" : T = 1 : ONERR GOTO 2075
+2072 ON -0.1 GOSUB 2073, 2074 : T = T + 5 : GOTO 2075
+2073 T = T + 2 : RETURN
+2074 T = T + 3 : RETURN
+2075 S = (T=1) AND (PEEK(222)=53): POKE 216,0 : GOSUB 1
+2076 T$ = "ON GOSUB (EDGE CASE: 255.2)" : T = 1 : ONERR GOTO 2080
+2077 ON 255.2 GOSUB 2078, 2079 : GOTO 2081
+2078 T = T + 2 : RETURN
+2079 T = T + 3 : RETURN
+2080 T = 255
+2081 S = (T=1) : POKE 216,0 : GOSUB 1
+2082 T$ = "ON GOSUB (EDGE CASE: 256)" : T = 1 : ONERR GOTO 2086
+2083 ON 256 GOSUB 2084, 2085 : T = T + 5 : GOTO 2086
+2084 T = T + 2 : RETURN
+2085 T = T + 3 : RETURN
+2086 S = (T=1) AND (PEEK(222)=53): POKE 216,0 : GOSUB 1
+
+2150 T$ = "POP" : T = 1 : GOSUB 2155 : T = T + 1 : GOTO 2159
+2155 T = T + 1 : GOSUB 2156 : T = T + 5
+2156 POP : T = T + 1 : RETURN
+2159 S = (T=4) : GOSUB 1
+
+2160 T$ = "FOR"
 : T = 0 : FOR I = 1 TO 10 : T = T + I : NEXT
 : S = (T = 55) : GOSUB 1
-2061 T$ = "FOR STEP"
+2161 T$ = "FOR STEP"
 : T = 0 : FOR I = 1 TO 10 STEP 2 : T = T + I : NEXT
 : S = (T = 25) : GOSUB 1
-2062 T$ = "FOR STEP"
+2162 T$ = "FOR STEP"
 : T = 0 : FOR I = 10 TO 1 STEP -1 : T = T + I : NEXT
 : S = (T = 55) : GOSUB 1
-2063 T$ = "FOR STEP"
+2163 T$ = "FOR STEP"
 : T = 0 : FOR I = 10 TO 1 : T = T + I : NEXT
 : S = (T = 10) : GOSUB 1
 
-2070 T$ = "NEXT"
+2170 T$ = "NEXT"
 : T = 0 : FOR I = 1 TO 10 : FOR J = 1 TO 10 : FOR K = 1 TO 10 : T = T + 1 : NEXT J, I
 : S = (T=100) : GOSUB 1
 
-2080 T$ = "IF THEN"
+2180 T$ = "IF THEN"
 : T = 1 : IF 0 THEN T = 2
-2081 S = (T=1) : GOSUB 1
+2181 S = (T=1) : GOSUB 1
 : T = 1 : IF 1 THEN T = 2 : T = 3
-2082 S = (T=3) : GOSUB 1
+2182 S = (T=3) : GOSUB 1
 
-2090 T$ = "IF GOTO"
-: T = 1 : IF 0 GOTO 2092 : T = 2
-2091 T = 3
-2092 S = (T=3) : GOSUB 1
-: T = 1 : IF 1 GOTO 2094 : T = 2
-2093 T = 3
-2094 S = (T=1) : GOSUB 1
+2190 T$ = "IF GOTO"
+: T = 1 : IF 0 GOTO 2192 : T = 2
+2191 T = 3
+2192 S = (T=3) : GOSUB 1
+: T = 1 : IF 1 GOTO 2194 : T = 2
+2193 T = 3
+2194 S = (T=1) : GOSUB 1
 
-2100 T$ = "Empty String is False"
+2200 T$ = "Empty String is False"
 : T = 1 : IF "" THEN T = 2
-2101 S = (T=1) : GOSUB 1
+2201 S = (T=1) : GOSUB 1
 
-2110 T$ = "Non-Empty String is True"
+2210 T$ = "Non-Empty String is True"
 : T = 1 : IF "abc" THEN T = 2
-2111 S = (T=2) : GOSUB 1
+2211 S = (T=2) : GOSUB 1
 
 
 3000 PRINT : PRINT "Error Handling ";