diff --git a/opcode.go b/opcode.go
index ac7feef5..bb32eeb9 100644
--- a/opcode.go
+++ b/opcode.go
@@ -688,7 +688,15 @@ func (pop *parsedOpcode) print(oneline bool) string {
 }
 
 func (pop *parsedOpcode) bytes() []byte {
-	retbytes := []byte{pop.opcode.value}
+	var retbytes []byte
+	if pop.opcode.length > 0 {
+		retbytes = make([]byte, 1, pop.opcode.length)
+	} else {
+		retbytes = make([]byte, 1, 1 + len(pop.data) -
+			pop.opcode.length)
+	}
+
+	retbytes[0] = pop.opcode.value
 	if pop.opcode.length == 1 {
 		return retbytes
 	}
@@ -708,11 +716,7 @@ func (pop *parsedOpcode) bytes() []byte {
 		}
 	}
 
-	for i := range pop.data {
-		retbytes = append(retbytes, pop.data[i])
-	}
-
-	return retbytes
+	return append(retbytes, pop.data...)
 }
 
 // opcode implementation functions from here
diff --git a/script.go b/script.go
index 581cf1eb..a74d19ef 100644
--- a/script.go
+++ b/script.go
@@ -274,7 +274,7 @@ func parseScript(script []byte) ([]parsedOpcode, error) {
 // template list for testing purposes. On error we return the list of parsed
 // opcodes so far.
 func parseScriptTemplate(script []byte, opcodemap map[byte]*opcode) ([]parsedOpcode, error) {
-	retScript := []parsedOpcode{}
+	retScript := make([]parsedOpcode, 0, len(script))
 	for i := 0; i < len(script); {
 		instr := script[i]
 		op, ok := opcodemap[instr]
@@ -329,7 +329,7 @@ func parseScriptTemplate(script []byte, opcodemap map[byte]*opcode) ([]parsedOpc
 // unparseScript reversed the action of parseScript and returns the
 // parsedOpcodes as a list of bytes
 func unparseScript(pops []parsedOpcode) []byte {
-	script := []byte{}
+	script := make([]byte, 0, len(pops))
 	for _, pop := range pops {
 		script = append(script, pop.bytes()...)
 	}
@@ -574,7 +574,7 @@ func (s *Script) subScript() []parsedOpcode {
 // removeOpcode will remove any opcode matching ``opcode'' from the opcode
 // stream in pkscript
 func removeOpcode(pkscript []parsedOpcode, opcode byte) []parsedOpcode {
-	retScript := []parsedOpcode{}
+	retScript := make([]parsedOpcode, 0, len(pkscript))
 	for _, pop := range pkscript {
 		if pop.opcode.value != opcode {
 			retScript = append(retScript, pop)
@@ -586,7 +586,7 @@ func removeOpcode(pkscript []parsedOpcode, opcode byte) []parsedOpcode {
 // removeOpcodeByData will return the pkscript minus any opcodes that would
 // push the data in ``data'' to the stack.
 func removeOpcodeByData(pkscript []parsedOpcode, data []byte) []parsedOpcode {
-	retScript := []parsedOpcode{}
+	retScript := make([]parsedOpcode, 0, len(pkscript))
 	for _, pop := range pkscript {
 		if !bytes.Equal(pop.data, data) {
 			retScript = append(retScript, pop)
diff --git a/test_coverage.txt b/test_coverage.txt
index a9469f3e..84fc677d 100644
--- a/test_coverage.txt
+++ b/test_coverage.txt
@@ -2,13 +2,13 @@
 github.com/conformal/btcscript/address.go	 scriptToAddressTemplate	 100.00% (58/58)
 github.com/conformal/btcscript/script.go	 Script.Step			 100.00% (37/37)
 github.com/conformal/btcscript/script.go	 parseScriptTemplate		 100.00% (30/30)
-github.com/conformal/btcscript/script.go	 NewScript			 100.00% (19/19)
+github.com/conformal/btcscript/script.go	 NewScript			 100.00% (18/18)
 github.com/conformal/btcscript/stack.go		 asInt				 100.00% (18/18)
 github.com/conformal/btcscript/stack.go		 fromInt			 100.00% (14/14)
+github.com/conformal/btcscript/opcode.go	 parsedOpcode.bytes		 100.00% (14/14)
 github.com/conformal/btcscript/opcode.go	 opcodeWithin			 100.00% (13/13)
-github.com/conformal/btcscript/script.go	 GetPreciseSigOpCount		 100.00% (13/13)
 github.com/conformal/btcscript/script.go	 isMultiSig			 100.00% (13/13)
-github.com/conformal/btcscript/opcode.go	 parsedOpcode.bytes		 100.00% (12/12)
+github.com/conformal/btcscript/script.go	 GetPreciseSigOpCount		 100.00% (13/13)
 github.com/conformal/btcscript/stack.go		 Stack.nipN			 100.00% (12/12)
 github.com/conformal/btcscript/opcode.go	 parsedOpcode.print		 100.00% (12/12)
 github.com/conformal/btcscript/opcode.go	 opcodeNotIf			 100.00% (11/11)
@@ -138,9 +138,9 @@ github.com/conformal/btcscript/opcode.go	 opcodeCheckMultiSig		 98.21% (55/56)
 github.com/conformal/btcscript/opcode.go	 opcodeCheckSig			 96.15% (25/26)
 github.com/conformal/btcscript/script.go	 Script.CheckErrorCondition	 78.57% (11/14)
 github.com/conformal/btcscript/opcode.go	 opcodeCheckSigVerify		 75.00% (3/4)
-github.com/conformal/btcscript/script.go	 Script.calcScriptHash		 71.43% (25/35)
+github.com/conformal/btcscript/script.go	 Script.calcScriptHash		 64.10% (25/39)
 github.com/conformal/btcscript/script.go	 Script.Execute			 44.44% (8/18)
 github.com/conformal/btcscript/log.go		 SetLogWriter			 0.00% (0/7)
 github.com/conformal/btcscript/log.go		 logClosure.String		 0.00% (0/1)
-github.com/conformal/btcscript			 --------------------------	 96.34% (896/930)
+github.com/conformal/btcscript			 --------------------------	 95.94% (897/935)