diff --git a/Dockerfile b/Dockerfile
index 04cc320..d77705c 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM fpco/stack-build:lts-20.14
+FROM fpco/stack-build:lts-21.25
 ENV TROUPE /Troupe
 ENV STACK_OPTS --system-ghc
 WORKDIR $TROUPE
diff --git a/compiler/src/Consts.hs b/compiler/src/Consts.hs
new file mode 100644
index 0000000..a0a3f45
--- /dev/null
+++ b/compiler/src/Consts.hs
@@ -0,0 +1,10 @@
+module Consts where
+
+-- * LLVM types
+
+-- | 2^31-1
+llvm_i32_maxBound :: Int
+llvm_i32_maxBound = 2147483647 
+
+llvm_maxIndex :: Int
+llvm_maxIndex = llvm_i32_maxBound
\ No newline at end of file
diff --git a/compiler/src/IR.hs b/compiler/src/IR.hs
index 70d9f3b..3ff20de 100644
--- a/compiler/src/IR.hs
+++ b/compiler/src/IR.hs
@@ -8,6 +8,7 @@
 
 module IR where
 
+import           Consts
 import qualified Basics
 import           RetCPS                    (VarName (..))
 
@@ -53,8 +54,7 @@ data IRExpr
   | WithRecord VarAccess Fields 
   | ProjField VarAccess Basics.FieldName
   -- | Projection of a tuple field at the given index. The maximum allowed index
-  -- is 2^53-1 (9007199254740991), the maximum representable number with 52 bits (unsigned),
-  -- as the runtime uses the IEEE 754 double-precision number format with a mantissa of 52 bits.
+  -- is 2^31-1 (2147483647).
   | ProjIdx VarAccess Word
   | List [VarAccess]
   -- | List cons of a value to a list.
@@ -331,8 +331,8 @@ instance WellFormedIRCheck IRExpr where
         then return ()
         else throwError $ "bad base function: " ++ fname
   wfir (ProjIdx _ idx) =
-    when (idx > 9007199254740991) $ -- 2^53-1
-      throwError $ "ProjIdx: illegal index: " ++ show idx ++ " (max index: 9007199254740991)"
+    when (idx > (fromIntegral Consts.llvm_maxIndex :: Word)) $
+      throwError $ "ProjIdx: illegal index: " ++ show idx ++ " (max index: " ++ show Consts.llvm_maxIndex ++ ")"
 
   wfir _ = return ()
 
diff --git a/compiler/stack.yaml b/compiler/stack.yaml
index 184ba5a..8fae81c 100644
--- a/compiler/stack.yaml
+++ b/compiler/stack.yaml
@@ -18,7 +18,7 @@
 #
 # resolver: ./custom-snapshot.yaml
 # resolver: https://example.com/snapshots/2018-01-01.yaml
-resolver: lts-20.14
+resolver: lts-21.25
 
 # User packages to be built.
 # Various formats can be used as shown in the example below.
diff --git a/tests/cmp/tuples_idx05b.golden b/tests/cmp/tuples_idx05b.golden
index 2a0f6a6..38d474a 100644
--- a/tests/cmp/tuples_idx05b.golden
+++ b/tests/cmp/tuples_idx05b.golden
@@ -1 +1 @@
-troupec: ProjIdx: illegal index: 9007199254740992 (max index: 9007199254740991)
+troupec: ProjIdx: illegal index: 2147483648 (max index: 2147483647)
diff --git a/tests/cmp/tuples_idx05b.trp b/tests/cmp/tuples_idx05b.trp
index 522c456..4b8dd9f 100644
--- a/tests/cmp/tuples_idx05b.trp
+++ b/tests/cmp/tuples_idx05b.trp
@@ -1 +1 @@
-(1,2,3).9007199254740992
\ No newline at end of file
+(1,2,3).2147483648
\ No newline at end of file
diff --git a/tests/rt/pos/core/tuples_idx05a.golden b/tests/rt/pos/core/tuples_idx05a.golden
index c3e4a61..c054345 100644
--- a/tests/rt/pos/core/tuples_idx05a.golden
+++ b/tests/rt/pos/core/tuples_idx05a.golden
@@ -1,3 +1,3 @@
 2024-02-14T11:33:50.114Z [RTM] info: Skipping network creation. Observe that all external IO operations will yield a runtime error.
 Runtime error in thread b490728b-03f4-4cbb-af4e-349efbca03d4@{}%{}
->> Index out of bounds: tuple (1@{}%{}, 2@{}%{}, 3@{}%{}) does not have length more than 9007199254740991
+>> Index out of bounds: tuple (1@{}%{}, 2@{}%{}, 3@{}%{}) does not have length more than 2147483647
diff --git a/tests/rt/pos/core/tuples_idx05a.trp b/tests/rt/pos/core/tuples_idx05a.trp
index 9fe5217..4e12ba7 100644
--- a/tests/rt/pos/core/tuples_idx05a.trp
+++ b/tests/rt/pos/core/tuples_idx05a.trp
@@ -1 +1 @@
-(1,2,3).9007199254740991
\ No newline at end of file
+(1,2,3).2147483647
\ No newline at end of file