diff --git a/tokenize/api.go b/tokenize/api.go
index 3de533a..7b084fb 100644
--- a/tokenize/api.go
+++ b/tokenize/api.go
@@ -149,18 +149,18 @@ func (tokenAPI *API) Fork() int {
 	if cap(frames) < (newStackLevel + 1) {
 		newFrames := make([]stackFrame, cap(frames)*2)
 		copy(newFrames, frames)
-		frames = newFrames
+		tokenAPI.stackFrames = newFrames
 	}
 
 	parent := tokenAPI.stackFrame
-	frames[newStackLevel] = stackFrame{
+	tokenAPI.stackFrames[newStackLevel] = stackFrame{
 		offset:     parent.offset,
 		bytesStart: parent.bytesEnd,
 		bytesEnd:   parent.bytesEnd,
 		tokenStart: parent.tokenEnd,
 		tokenEnd:   parent.tokenEnd,
 	}
-	tokenAPI.stackFrame = &frames[newStackLevel]
+	tokenAPI.stackFrame = &tokenAPI.stackFrames[newStackLevel]
 
 	return newStackLevel
 }
@@ -205,16 +205,19 @@ func (tokenAPI *API) Merge(stackLevel int) {
 	parent.tokenEnd = f.tokenEnd
 	f.tokenStart = f.tokenEnd
 
+	// Update the parent read offset.
 	parent.offset = f.offset
+
+	// Update the parent cursor position.
 	if f.line > parent.line {
 		parent.line += f.line
 		parent.column = f.column
 	} else {
 		parent.column += f.column
 	}
+
 	f.line = 0
 	f.column = 0
-
 	f.err = nil
 }
 
@@ -223,32 +226,19 @@ func (tokenAPI *API) Merge(stackLevel int) {
 // cleared as well.
 func (tokenAPI *API) Reset() {
 	f := tokenAPI.stackFrame
-	if tokenAPI.stackLevel == 0 {
-		f.column = 0
-		f.line = 0
-		f.offset = 0
-	} else {
-		parent := tokenAPI.stackFrames[tokenAPI.stackLevel-1]
-		f.column = 0
-		f.line = 0
-		f.offset = parent.offset
-	}
 	f.bytesEnd = f.bytesStart
 	f.tokenEnd = f.tokenStart
+	f.column = 0
+	f.line = 0
+	if tokenAPI.stackLevel == 0 {
+		f.offset = 0
+	} else {
+		f.offset = tokenAPI.stackFrames[tokenAPI.stackLevel-1].offset
+	}
 	f.err = nil
 }
 
 func (tokenAPI *API) Dispose(stackLevel int) {
-	if stackLevel == 0 {
-		callerPanic("Dispose", "tokenize.API.{name}(): {name}() called at {caller} "+
-			"on the top-level API stack level 0")
-	}
-	if stackLevel != tokenAPI.stackLevel {
-		callerPanic("Dispose", "tokenize.API.{name}(): {name}() called at {caller} "+
-			"on API stack level %d, but the current stack level is %d "+
-			"(forgot to Dispose() a forked child?)", stackLevel, tokenAPI.stackLevel)
-	}
-
 	tokenAPI.stackLevel = stackLevel - 1
 	tokenAPI.stackFrame = &tokenAPI.stackFrames[stackLevel-1]
 }