diff --git a/README.md b/README.md
index 2922a35..4d303f5 100644
--- a/README.md
+++ b/README.md
@@ -21,8 +21,7 @@ Pkg.add("INMET")
 The INMET API requires a token, which can be requested by sending an e-mail
 to [cadastro.act@inmet.gov.br](mailto:cadastro.act@inmet.gov.br).
 
-Save the token in an environment variable `INMET_TOKEN` to conclude
-the installation.
+Save the token in an environment variable `INMET_TOKEN` to use this package.
 
 ## Usage
 
diff --git a/src/INMET.jl b/src/INMET.jl
index 54aa8a4..a672086 100644
--- a/src/INMET.jl
+++ b/src/INMET.jl
@@ -11,18 +11,6 @@ import Unitful: °, m, °C, percent
 
 export Date, DateTime
 
-function __init__()
-  if !haskey(ENV, "INMET_TOKEN")
-    @warn """
-    The INMET API requires a token, which can be requested by sending an e-mail
-    to [cadastro.act@inmet.gov.br](mailto:cadastro.act@inmet.gov.br).
-
-    Save the token in an environment variable `INMET_TOKEN` to conclude
-    the installation.
-    """
-  end
-end
-
 # -----------
 # PUBLIC API
 # -----------
@@ -58,7 +46,7 @@ function series(station, start, finish, freq=:day)
   kind = freq == :day ? "diaria" : ""
   from = string(start)
   to   = string(finish)
-  token = ENV["INMET_TOKEN"]
+  token = inmettoken()
   url = "https://apitempo.inmet.gov.br/token/estacao/$kind/$from/$to/$station/$token"
   url |> download |> frame
 end
@@ -74,7 +62,7 @@ hour information is retained (data in hourly frequency).
 function on(time)
   date = string(Date(time))
   hour = time isa DateTime ? (@sprintf "%02d00" Dates.hour(time)) : "0000"
-  token = ENV["INMET_TOKEN"]
+  token = inmettoken()
   url = "https://apitempo.inmet.gov.br/token/estacao/dados/$date/$hour/$token"
   url |> download |> frame
 end
@@ -83,6 +71,18 @@ end
 # HELPER FUNCTIONS
 # -----------------
 
+function inmettoken()
+  if !haskey(ENV, "INMET_TOKEN")
+    throw(ErrorException("""
+    The INMET API requires a token, which can be requested by sending an e-mail
+    to [cadastro.act@inmet.gov.br](mailto:cadastro.act@inmet.gov.br).
+
+    Save the token in an environment variable `INMET_TOKEN` to use this package.
+    """))
+  end
+  ENV["INMET_TOKEN"]
+end
+
 function download(url)
   page = HTTP.get(url)
   str  = String(page.body)
diff --git a/test/runtests.jl b/test/runtests.jl
index 3a0da8e..2b24a6e 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -13,16 +13,25 @@ using Test
   end
 
   @testset "series" begin
-    df = INMET.series(:A301, Date(2021,1,1), Date(2021,7,31))
-    @test all(isequal("A301"), df.CD_ESTACAO)
+    if haskey(ENV, "INMET_TOKEN")
+      df = INMET.series(:A301, Date(2021,1,1), Date(2021,7,31))
+      @test all(isequal("A301"), df.CD_ESTACAO)
+    else
+      @test_throws ErrorException INMET.series(:A301, Date(2021,1,1), Date(2021,7,31))
+    end
   end
 
   @testset "on" begin
-    dfday  = INMET.on(Date(2021,7,1))
-    dfhour = INMET.on(DateTime(2021,7,1,1))
-    @test size(dfday, 1) > size(dfhour, 1)
-    @test all(isequal("2021-07-01"), dfday.DT_MEDICAO)
-    @test all(isequal("2021-07-01"), dfhour.DT_MEDICAO)
-    @test all(isequal("0100"), dfhour.HR_MEDICAO)
+    if haskey(ENV, "INMET_TOKEN")
+      dfday  = INMET.on(Date(2021,7,1))
+      dfhour = INMET.on(DateTime(2021,7,1,1))
+      @test size(dfday, 1) > size(dfhour, 1)
+      @test all(isequal("2021-07-01"), dfday.DT_MEDICAO)
+      @test all(isequal("2021-07-01"), dfhour.DT_MEDICAO)
+      @test all(isequal("0100"), dfhour.HR_MEDICAO)
+    else
+      @test_throws ErrorException INMET.on(Date(2021,7,1))
+      @test_throws ErrorException INMET.on(Date(2021,7,1))
+    end
   end
 end