diff --git a/R/stat-smooth.r b/R/stat-smooth.r
index 6dc63cc647..3b3ba735e7 100644
--- a/R/stat-smooth.r
+++ b/R/stat-smooth.r
@@ -108,7 +108,7 @@ StatSmooth <- ggproto("StatSmooth", Stat,
       } else {
         params$formula <- y ~ x
       }
-      msg <- c(msg, paste0("formula '", deparse(params$formula), "'"))
+      msg <- c(msg, paste0("formula = '", deparse(params$formula), "'"))
     }
     if (identical(params$method, "gam")) {
       params$method <- mgcv::gam
diff --git a/tests/testthat/test-geom-smooth.R b/tests/testthat/test-geom-smooth.R
index a317d78e07..242742763c 100644
--- a/tests/testthat/test-geom-smooth.R
+++ b/tests/testthat/test-geom-smooth.R
@@ -42,7 +42,7 @@ test_that("default smoothing methods for small and large data sets work", {
 
   expect_message(
     plot_data <- layer_data(p),
-    "method = 'loess' and formula 'y ~ x'"
+    "method = 'loess' and formula = 'y ~ x'"
   )
   expect_equal(plot_data$y, as.numeric(out))
 
@@ -61,7 +61,7 @@ test_that("default smoothing methods for small and large data sets work", {
 
   expect_message(
     plot_data <- layer_data(p),
-    "method = 'gam' and formula 'y ~ s\\(x, bs = \"cs\"\\)"
+    "method = 'gam' and formula = 'y ~ s\\(x, bs = \"cs\"\\)"
   )
   expect_equal(plot_data$y, as.numeric(out))
 
@@ -70,7 +70,7 @@ test_that("default smoothing methods for small and large data sets work", {
 
   expect_message(
     plot_data <- layer_data(p),
-    "method = 'gam' and formula 'y ~ s\\(x, bs = \"cs\"\\)"
+    "method = 'gam' and formula = 'y ~ s\\(x, bs = \"cs\"\\)"
   )
   expect_equal(plot_data$y, as.numeric(out))
 })