diff --git a/compiler/basicTypes/MkId.hs b/compiler/basicTypes/MkId.hs
index e146c66c47be76dc2289109b0dfbadf01a7c47ff..99a4d2513357a23f1b58af819f3023fe0a9bb2a3 100644
--- a/compiler/basicTypes/MkId.hs
+++ b/compiler/basicTypes/MkId.hs
@@ -393,7 +393,7 @@ mkDataConWorkId wkr_name data_con
         -- the simplifier thinks that y is "sure to be evaluated" (because
         --  $wMkT is strict) and drops the case.  No, $wMkT is not strict.
         --
-        -- When the simplifer sees a pattern
+        -- When the simplifier sees a pattern
         --      case e of MkT x -> ...
         -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
         -- but that's fine... dataConRepStrictness comes from the data con
diff --git a/compiler/coreSyn/CoreLint.hs b/compiler/coreSyn/CoreLint.hs
index d905b8cc41fdf6a33d67a7877811b937a8e26cf8..06e45830e72cacb592503e6a00e46d8216eae512 100644
--- a/compiler/coreSyn/CoreLint.hs
+++ b/compiler/coreSyn/CoreLint.hs
@@ -891,7 +891,7 @@ checkCaseAlts :: CoreExpr -> OutType -> [CoreAlt] -> LintM ()
 -- b2) Check that the others are in increasing order
 -- c) Check that there's a default for infinite types
 -- NB: Algebraic cases are not necessarily exhaustive, because
---     the simplifer correctly eliminates case that can't
+--     the simplifier correctly eliminates case that can't
 --     possibly match.
 
 checkCaseAlts e ty alts =
diff --git a/compiler/simplCore/OccurAnal.hs b/compiler/simplCore/OccurAnal.hs
index 33e0c45140a188004f9a6417590c5cad4680e5a1..2efd82f62069f7c6f4e7d3f4e456a770667cdebe 100644
--- a/compiler/simplCore/OccurAnal.hs
+++ b/compiler/simplCore/OccurAnal.hs
@@ -958,7 +958,7 @@ reOrderNodes depth bndr_set weak_fvs (node : nodes) binds
         | otherwise = 0
 
         -- Checking for a constructor application
-        -- Cheap and cheerful; the simplifer moves casts out of the way
+        -- Cheap and cheerful; the simplifier moves casts out of the way
         -- The lambda case is important to spot x = /\a. C (f a)
         -- which comes up when C is a dictionary constructor and
         -- f is a default method.
diff --git a/compiler/simplCore/Simplify.hs b/compiler/simplCore/Simplify.hs
index 6e6a6aa424cfb1d62367a4c6e3d21f09e2d87ffe..bd0c8a9dfaada51c9a3181d0b7c91e09dd9a6f02 100644
--- a/compiler/simplCore/Simplify.hs
+++ b/compiler/simplCore/Simplify.hs
@@ -2320,7 +2320,7 @@ knownCon env scrut dc dc_ty_args dc_args bndr bs rhs cont
 -------------------
 missingAlt :: SimplEnv -> Id -> [InAlt] -> SimplCont -> SimplM (SimplEnv, OutExpr)
                 -- This isn't strictly an error, although it is unusual.
-                -- It's possible that the simplifer might "see" that
+                -- It's possible that the simplifier might "see" that
                 -- an inner case has no accessible alternatives before
                 -- it "sees" that the entire branch of an outer case is
                 -- inaccessible.  So we simply put an error case here instead.
diff --git a/compiler/specialise/Specialise.hs b/compiler/specialise/Specialise.hs
index abd15c8564f6e15cbd0537c89673a6f18db6f35d..644ecc7d436f29c5bac31b6425cf4afb1c0d9181 100644
--- a/compiler/specialise/Specialise.hs
+++ b/compiler/specialise/Specialise.hs
@@ -398,7 +398,7 @@ Seems quite reasonable.  Similar things could be done with instance decls:
 Ho hum.  Things are complex enough without this.  I pass.
 
 
-Requirements for the simplifer
+Requirements for the simplifier
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The simplifier has to be able to take advantage of the specialisation.
 
@@ -1356,7 +1356,7 @@ crash. So we use Refl right off the bat, and do not forall-quantify 'g':
  * exprsFreeIdsList returns the Ids bound by the args,
    which won't include g
 
-You might wonder if this will match as often, but the simplifer replaces
+You might wonder if this will match as often, but the simplifier replaces
 complicated Refl coercions with Refl pretty aggressively.
 
 Note [Orphans and auto-generated rules]
diff --git a/testsuite/tests/dependent/should_compile/dynamic-paper.hs b/testsuite/tests/dependent/should_compile/dynamic-paper.hs
index 838155242cebf2b69411a07503f90292d45be9aa..0d55bba93a5d05d5558828e27e0f59c176dd7ab9 100644
--- a/testsuite/tests/dependent/should_compile/dynamic-paper.hs
+++ b/testsuite/tests/dependent/should_compile/dynamic-paper.hs
@@ -2,7 +2,7 @@
 Stephanie Weirich, Richard Eisenberg, and Dimitrios Vytiniotis, 2016. -}
 
 -- NB: it includes a negative-recursive function (see delta1), and
--- so will give "simplifer ticks exhausted", at least with -O
+-- so will give "simplifier ticks exhausted", at least with -O
 
 {-#  LANGUAGE RankNTypes, PolyKinds, TypeOperators,
              ScopedTypeVariables, GADTs, FlexibleInstances,