ggplot adds backticks to labels (see x-axis label). The behavior was different in previous versions (e.g., 2.2.1). ``` r library(ggplot2) d <- data.frame(rnorm(100)) colnames(d) <- 'a b' ggplot(d, aes(`a b`)) + geom_histogram() #> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`. ```  Created on 2018-11-01 by the [reprex package](http://reprex.tidyverse.org) (v0.2.0).