diff --git a/README.md b/README.md
index 25bd8bb..ca8eca6 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ To assemble `src/main.etk` you will need to invoke `eas`:
 
 ```console
 $ eas src/main.etk
-3373fffffffffffffffffffffffffffffffffffffffe14604457602036146024575f5ffd5b620180005f350680545f35146037575f5ffd5b6201800001545f5260205ff35b6201800042064281555f359062018000015500
+3373fffffffffffffffffffffffffffffffffffffffe14604d57602036146024575f5ffd5b5f35801560495762016da0810690815414603c575f5ffd5b62016da001545f5260205ff35b5f5ffd5b62016da042064281555f359062016da0015500
 ```
 
 It's also possible to remove the `etk` preproccessing by doing a roundtrip --
@@ -31,7 +31,7 @@ $ disease --code 0x$(eas src/main.etk)
    0:   caller
    1:   push20 0xfffffffffffffffffffffffffffffffffffffffe
   16:   eq
-  17:   push1 0x44
+  17:   push1 0x4d
   19:   jumpi
 
   1a:   push1 0x20
@@ -45,46 +45,57 @@ $ disease --code 0x$(eas src/main.etk)
   23:   revert
 
   24:   jumpdest
-  25:   push3 0x018000
-  29:   push0
-  2a:   calldataload
-  2b:   mod
-  2c:   dup1
-  2d:   sload
-  2e:   push0
-  2f:   calldataload
-  30:   eq
-  31:   push1 0x37
-  33:   jumpi
-
-  34:   push0
-  35:   push0
-  36:   revert
-
-  37:   jumpdest
-  38:   push3 0x018000
-  3c:   add
-  3d:   sload
-  3e:   push0
-  3f:   mstore
-  40:   push1 0x20
-  42:   push0
-  43:   return
-
-  44:   jumpdest
-  45:   push3 0x018000
-  49:   timestamp
-  4a:   mod
-  4b:   timestamp
-  4c:   dup2
-  4d:   sstore
-  4e:   push0
-  4f:   calldataload
-  50:   swap1
-  51:   push3 0x018000
-  55:   add
+  25:   push0
+  26:   calldataload
+  27:   dup1
+  28:   iszero
+  29:   push1 0x49
+  2b:   jumpi
+
+  2c:   push3 0x016da0
+  30:   dup2
+  31:   mod
+  32:   swap1
+  33:   dup2
+  34:   sload
+  35:   eq
+  36:   push1 0x3c
+  38:   jumpi
+
+  39:   push0
+  3a:   push0
+  3b:   revert
+
+  3c:   jumpdest
+  3d:   push3 0x016da0
+  41:   add
+  42:   sload
+  43:   push0
+  44:   mstore
+  45:   push1 0x20
+  47:   push0
+  48:   return
+
+  49:   jumpdest
+  4a:   push0
+  4b:   push0
+  4c:   revert
+
+  4d:   jumpdest
+  4e:   push3 0x016da0
+  52:   timestamp
+  53:   mod
+  54:   timestamp
+  55:   dup2
   56:   sstore
-  57:   stop
+  57:   push0
+  58:   calldataload
+  59:   swap1
+  5a:   push3 0x016da0
+  5e:   add
+  5f:   sstore
+  60:   stop
+
 ```
 
 ### Control-flow Graph
diff --git a/docs/cfg.png b/docs/cfg.png
index cbaff78..67c2fdc 100644
Binary files a/docs/cfg.png and b/docs/cfg.png differ
diff --git a/src/main.etk b/src/main.etk
index 61c158e..5acde1e 100644
--- a/src/main.etk
+++ b/src/main.etk
@@ -29,7 +29,7 @@
 
 # buflen returns the HISTORY_BUFFER_LENGTH as defined in the EIP.
 %def buflen()
-        98304
+        93600
 %end
 
 # sysaddr is the address which calls the contract to submit a new root.
@@ -37,14 +37,8 @@
         0xfffffffffffffffffffffffffffffffffffffffe
 %end
 
-# get_input loads the first word of input from calldata.
-%macro get_input()
-        push0           # [0]
-        calldataload    # [calldata[0..32]]
-%end
-
-# revert sets up and then executes a revert instruction.
-%macro revert()
+# do_revert sets up and then executes a revert(0,0) operation.
+%macro do_revert()
         push0           # [0]
         push0           # [0, 0]
         revert          # []
@@ -74,31 +68,40 @@ start:
         # Jump to continue if length-check passed, otherwise revert.
         push1 loadtime   # [loadtime_lbl, calldatasize == 32]
         jumpi            # []
-        %revert()        # []
-
+        %do_revert()     # []
 
 loadtime:
+        jumpdest
+
+        # Load input timestamp.
+        push0            # [0]
+        calldataload     # [input_timestamp]
+        dup1             # [input_timestamp, input_timestamp]
+
+        # Verify input timestamp is non-zero.
+        iszero           # [input_timestamp == 0, input_timestamp]
+        push1 throw      # [throw_lbl, input_timestamp == 0, input_timestamp]
+        jumpi            # [input_timestamp]
+
         # Compute the timestamp index and load from storage.
-        jumpdest         # []
-        push3 buflen()   # [buflen]
-        %get_input()     # [time, buflen]
-        mod              # [time_index]
-        dup1             # [time_index, time_index]
-        sload            # [timestamp, time_index]
+        push3 buflen()   # [buflen, input_timestamp]
+        dup2             # [input_timestamp, buflen, input_timestamp]
+        mod              # [time_index, input_timestamp]
+        swap1            # [input_timestamp, time_index]
+        dup2             # [time_index, input_timestamp, time_index]
+        sload            # [stored_timestamp, input_timestamp, time_index]
 
         # Verify stored timestamp matches input timestamp. It's possible these
         # don't match if the slot has been overwritten by the ring buffer or if
         # the timestamp input wasn't a valid previous timestamp.
-        %get_input()     # [input, timestamp, time_index]
-        eq               # [input == timestamp, time_index]
+        eq               # [stored_timestamp == input_timestamp, time_index]
         push1 loadroot   # [loadroot_lbl, input == timestamp, time_index]
         jumpi            # [time_index]
-        %revert()        # []
-
+        %do_revert()     # []
 
 loadroot:
         # Extend index to get root index.
-        jumpdest
+        jumpdest         # [time_index]
         push3 buflen()   # [buflen, time_index]
         add              # [root_index]
         sload            # [root]
@@ -112,6 +115,11 @@ loadroot:
         push0            # [offset, size]
         return           # []
 
+throw:
+        # Reverts current execution with no return data.
+        jumpdest
+        %do_revert()
+
 submit:
         jumpdest         # []
 
diff --git a/test/Contract.t.sol.in b/test/Contract.t.sol.in
index 6123596..91e50a2 100644
--- a/test/Contract.t.sol.in
+++ b/test/Contract.t.sol.in
@@ -6,7 +6,7 @@ import "../src/Contract.sol";
 
 address constant addr = 0x000000000000000000000000000000000000000b;
 address constant sysaddr = 0xffffFFFfFFffffffffffffffFfFFFfffFFFfFFfE;
-uint256 constant buflen = 98304;
+uint256 constant buflen = 93600;
 bytes32 constant root    = hex"88e96d4537bea4d9c05d12549907b32561d3bf31f45aae734cdc119f13406cb6";
 
 function timestamp() view returns (bytes32) {
@@ -87,6 +87,11 @@ contract ContractTest is Test {
         (ret, data) = unit.call(bytes.concat(bytes32(time+1)));
         assertFalse(ret);
         assertEq(data, hex"");
+
+        // Timestamp zero should fail.
+        (ret, data) = unit.call(bytes.concat(bytes32(0)));
+        assertFalse(ret);
+        assertEq(data, hex"");
     }
 
     // testUpdate verifies the set functionality of the contract.
@@ -137,7 +142,7 @@ contract ContractTest is Test {
         uint256 start = block.timestamp;
 
         // Saturate storage with fake roots.
-        for (uint256 i = 0; i < 8192; i += 1) {
+        for (uint256 i = 0; i < buflen / 12; i += 1) {
             bytes32 pbbr = bytes32(i*1337);
             vm.prank(sysaddr);
             (bool ret, bytes memory data) = unit.call(bytes.concat(pbbr));
@@ -147,7 +152,7 @@ contract ContractTest is Test {
         }
 
         // Attempt to read all values in same block context.
-        for (uint256 i = 0; i < 8192; i += 1) {
+        for (uint256 i = 0; i < buflen / 12; i += 1) {
             bytes32 time = bytes32(uint256(start+i*12));
             (bool ret, bytes memory got) = unit.call(bytes.concat(time));
             assertTrue(ret);