diff --git a/DESCRIPTION b/DESCRIPTION
index 4166d09d269f151f3cb6dfb8fdb40e408ac39932..2e9044b9d0e6c63877498ae38f95c47b6ed75fa6 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: airGR
 Type: Package
 Title: Suite of GR Hydrological Models for Precipitation-Runoff Modelling
-Version: 1.6.8.25
+Version: 1.6.8.26
 Date: 2020-12-02
 Authors@R: c(
   person("Laurent", "Coron", role = c("aut", "trl"), comment = c(ORCID = "0000-0002-1503-6204")),
diff --git a/R/SeriesAggreg.data.frame.R b/R/SeriesAggreg.data.frame.R
index ad37d16b08bb85b049ec5c1d96811dd09934ff0d..12c4184f8a8cc20ac5e6ec9d6b4b2c26fca531a9 100644
--- a/R/SeriesAggreg.data.frame.R
+++ b/R/SeriesAggreg.data.frame.R
@@ -102,10 +102,16 @@ SeriesAggreg.data.frame <- function(x,
     stop  <-
       sprintf("%i-12-31 00:00:00", as.numeric(format(TabSeries2$DatesR[nrow(TabSeries2)], format = "%Y")) +
                 1)
-    by <-
-      ifelse(grepl("hours", format(diff(
-        x$DatesR[1:2]
-      ))), yes = "hours", no = "days")
+    Ts <- format(diff(x$DatesR[1:2]))
+    if(gsub("[0-9]+ ", "", Ts) == "hours") {
+      by <- "hours"
+    } else {
+      if(gsub(" days$", "", Ts) == "1") {
+        by <- "days"
+      } else {
+        by <- "months"
+      }
+    }
     fakeTs <-
       data.frame(DatesR = seq(
         from = as.POSIXct(start, tz = "UTC"),
diff --git a/tests/testthat/test-SeriesAggreg.R b/tests/testthat/test-SeriesAggreg.R
index 3c84e4e3a465871d9d7ffaa6c87ff6bffa046dc1..50994219c21d5c3c45143839f348148530f3b60c 100644
--- a/tests/testthat/test-SeriesAggreg.R
+++ b/tests/testthat/test-SeriesAggreg.R
@@ -194,6 +194,6 @@ test_that("SeriesAggreg from and to the same time step should return initial tim
     PotEvap = BasinObs$E
   )
   I2 <- SeriesAggreg(InputsModel, "%Y%m")
-  I3 <- SeriesAggreg(I2, "%Y%m")
-  expect_equal(I2, I3)
+  expect_warning(SeriesAggreg(I2, "%Y%m"), regexp = "No time-step conversion was performed")
+  expect_equal(I2, suppressWarnings(SeriesAggreg(I2, "%Y%m")))
 })