Need to fill data frame with missing years and value in 2nd column

Question

I have data frames with counts from a series of years, 1970-2020, generated by a subset command from a larger data set, i.e. resulting in two columns "Year" and "Count":

Year         Count
1987         8
1989         1
1991         1
1992         4
1995         11
1996         3
1997         7
.
.
.
2019         2
2020         5

There are missing years where Count=0, and I need a procedure to fill these df's with the missing years and Count=0. I have this script that I can't get to work:

library(tidyr)
aug <- subset(mainframe, month==8)
complete(aug, year = 1987:2020, fill = list(Count = 0))

Here's a sample dataframe 'aug':

dput(aug)
structure(list(month = structure(c(8L, 8L, 8L, 8L, 8L, 8L, 8L, 
8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 
8L, 8L, 8L, 8L, 8L), .Label = c("1", "2", "3", "4", "5", "6", 
"7", "8", "9", "10", "11", "12"), class = "factor"), year = structure(1:28, .Label = c("1987", 
"1988", "1989", "1990", "1991", "1992", "1993", "1994", "1995", 
"1996", "1998", "2000", "2001", "2002", "2003", "2004", "2005", 
"2006", "2007", "2008", "2009", "2010", "2011", "2013", "2015", 
"2016", "2018", "2020"), class = "factor"), Count = c(4L, 0L, 
3L, 3L, 0L, 0L, 1L, 0L, 1L, 1L, 3L, 0L, 0L, 0L, 0L, 2L, 0L, 0L, 
0L, 2L, 0L, 1L, 1L, 0L, 0L, 1L, 0L, 1L)), row.names = c(8L, 20L, 
32L, 44L, 56L, 68L, 80L, 92L, 104L, 116L, 128L, 140L, 152L, 164L, 
176L, 188L, 200L, 212L, 224L, 236L, 248L, 260L, 272L, 284L, 296L, 
308L, 320L, 332L), class = "data.frame")