diff --git a/hledger-lib/Hledger/Write/Beancount.hs b/hledger-lib/Hledger/Write/Beancount.hs
index e0e1d3302..5c5666086 100644
--- a/hledger-lib/Hledger/Write/Beancount.hs
+++ b/hledger-lib/Hledger/Write/Beancount.hs
@@ -10,6 +10,7 @@ module Hledger.Write.Beancount (
   -- postingAsLinesBeancount,
   -- showAccountNameBeancount,
   accountNameToBeancount,
+  commodityToBeancount,
   -- beancountTopLevelAccounts,
 
   -- * Tests
diff --git a/hledger/Hledger/Cli/Commands/Print.hs b/hledger/Hledger/Cli/Commands/Print.hs
index a2e53fe91..d36fbac42 100644
--- a/hledger/Hledger/Cli/Commands/Print.hs
+++ b/hledger/Hledger/Cli/Commands/Print.hs
@@ -44,7 +44,8 @@ import Hledger.Cli.Utils
 import Hledger.Cli.Anchor (setAccountAnchor)
 import qualified Lucid
 import qualified System.IO as IO
-import Data.Maybe (isJust)
+import Data.Maybe (isJust, catMaybes)
+import Hledger.Write.Beancount (commodityToBeancount)
 
 printmode = hledgerCommandMode
   $(embedFileRelative "Hledger/Cli/Commands/Print.txt")
@@ -183,11 +184,17 @@ entriesReportAsTextHelper :: (Transaction -> T.Text) -> EntriesReport -> TL.Text
 entriesReportAsTextHelper showtxn = TB.toLazyText . foldMap (TB.fromText . showtxn)
 
 -- This transforms transactions in various ways (see Beancount.hs) to make them Beancount-compatible.
--- It also generates an account open directive for each account used (on their earliest transaction dates).
+-- It also generates an account open directive for each account used (on their earliest transaction dates),
+-- and operating_currency directives based on currencies used in costs.
 entriesReportAsBeancount :: EntriesReport -> TL.Text
 entriesReportAsBeancount ts =
   -- PERF: gathers and converts all account names, then repeats that work when showing each transaction
-  opendirectives <> "\n" <> entriesReportAsTextHelper showTransactionBeancount ts3
+  TL.concat [
+     TL.fromStrict operatingcurrencydirectives
+    ,TL.fromStrict openaccountdirectives
+    ,"\n"
+    ,entriesReportAsTextHelper showTransactionBeancount ts3
+    ]
   where
     -- Remove any virtual postings.
     ts2 = [t{tpostings=filter isReal $ tpostings t} | t <- ts]
@@ -198,7 +205,7 @@ entriesReportAsBeancount ts =
     ts3 =
       [ t{tpostings=filter (not . isredundantconvp) $ tpostings t}
       | t <- ts2
-      -- XXX But how to do it ? conversion-posting tag is on non-redundant postings too.
+      -- XXX But conversion-posting tag is on non-redundant postings too, so how to do it ?
       -- Assume the simple case of no more than one cost + conversion posting group in each transaction.
       -- Actually that seems to be required by hledger right now.
       , let isredundantconvp p =
@@ -206,9 +213,48 @@ entriesReportAsBeancount ts =
               && any (any (isJust.acost) . amounts . pamount) (tpostings t)
       ]
 
-    opendirectives
+    -- https://fava.pythonanywhere.com/example-beancount-file/help/beancount_syntax
+    -- https://fava.pythonanywhere.com/example-beancount-file/help/options
+    -- "conversion-currencies
+    -- When set, the currency conversion select dropdown in all charts will show the list of currencies specified in this option.
+    -- By default, Fava lists all operating currencies and those currencies that match ISO 4217 currency codes."
+
+    -- http://furius.ca/beancount/doc/syntax
+    -- http://furius.ca/beancount/doc/options
+    -- "This option may be supplied multiple times ...
+    -- A list of currencies that we single out during reporting and create dedicated columns for ...
+    -- we use this to display these values in table cells without their associated unit strings ...
+    -- This is used to indicate the main currencies that you work with in real life"
+    -- We use: all currencies used in costs.
+    operatingcurrencydirectives
+      | null basecurrencies = ""
+      | otherwise = T.unlines (map (todirective . commodityToBeancount) basecurrencies) <> "\n"
+      where
+        todirective c = "option \"operating_currency\" \"" <> c <> "\""
+        basecurrencies = allcostcurrencies
+          where
+            allcostcurrencies = nubSort $ map acommodity costamounts
+              where
+                costamounts =
+                  map (\c -> case c of
+                              UnitCost  a -> a
+                              TotalCost a -> a
+                              ) $ 
+                  catMaybes $
+                  map acost $
+                  concatMap (amounts . pamount) $
+                  concatMap tpostings
+                  ts3
+
+    -- http://furius.ca/beancount/doc/syntax
+    -- "there exists an “Open” directive that is used to provide the start date of each account. 
+    -- That can be located anywhere in the file, it does not have to appear in the file somewhere before you use an account name.
+    -- You can just start using account names in transactions right away,
+    -- though all account names that receive postings to them will eventually have to have
+    -- a corresponding Open directive with a date that precedes all transactions posted to the account in the input file."
+    openaccountdirectives
       | null ts = ""
-      | otherwise = TL.fromStrict $ T.unlines [
+      | otherwise = T.unlines [
           firstdate <> " open " <> accountNameToBeancount a
           | a <- nubSort $ concatMap (map paccount.tpostings) ts3
           ]
diff --git a/hledger/hledger.m4.md b/hledger/hledger.m4.md
index f4f7d860b..2facc8066 100644
--- a/hledger/hledger.m4.md
+++ b/hledger/hledger.m4.md
@@ -875,8 +875,9 @@ Currently we support at most one cost + conversion postings group per transactio
 
 #### Beancount operating currency
 
-Declaring an operating currency improves Beancount and Fava reports.
-You can do this manually by adding a line like this to the beancount journal:
+Declaring an operating currency (or several) improves Beancount and Fava reports.
+Currently hledger will declare each currency used in cost amounts as an operating currency.
+If needed, replace these with your own declaration, like
 ```beancount
 option "operating_currency" "USD"
 ```
diff --git a/hledger/test/print/beancount.test b/hledger/test/print/beancount.test
index a77f88c93..4521a6423 100644
--- a/hledger/test/print/beancount.test
+++ b/hledger/test/print/beancount.test
@@ -85,6 +85,7 @@ $ hledger -f- print -O beancount
 >=
 
 # ** 6. Conversion postings that are redundant with costs are dropped.
+# And when there are costs, operating_currency directives are added for the cost currencies.
 <
 2000-01-01
     Assets                      $1 @@ €1
@@ -93,6 +94,8 @@ $ hledger -f- print -O beancount
     Assets                     €-1
 
 $ hledger -f- print -O beancount
+option "operating_currency" "EUR"
+
 2000-01-01 open Assets:A
 
 2000-01-01 *