diff --git a/src/core/Function.go b/src/core/Function.go
index 37024df..1241c9f 100644
--- a/src/core/Function.go
+++ b/src/core/Function.go
@@ -23,6 +23,7 @@ type Function struct {
 	name          string
 	pkg           string
 	body          token.Source
+	constantStack []*Constant
 	valueToStruct map[ssa.Value]*ssa.Struct
 	loopStack
 	ssa.IR
diff --git a/src/core/errors_test.go b/src/core/errors_test.go
index 26d7809..c635c81 100644
--- a/src/core/errors_test.go
+++ b/src/core/errors_test.go
@@ -23,6 +23,8 @@ var errs = []struct {
 	{"AlwaysFalse2.q", core.AlwaysFalse},
 	{"AlwaysFalse3.q", core.AlwaysFalse},
 	{"AlwaysFalse4.q", core.AlwaysFalse},
+	// {"CycleDetected.q", &core.CycleDetected{A: "A", B: "B"}}, // TODO: deterministic output
+	{"CycleDetected2.q", &core.CycleDetected{A: "y", B: "x"}},
 	{"DefinitionCountMismatch.q", &core.DefinitionCountMismatch{Function: "main.swap", Count: 1, ExpectedCount: 2}},
 	{"DefinitionCountMismatch2.q", &core.DefinitionCountMismatch{Function: "main.swap", Count: 3, ExpectedCount: 2}},
 	{"DefinitionCountMismatch3.q", &core.DefinitionCountMismatch{Function: "main.nothing", Count: 1, ExpectedCount: 0}},
diff --git a/src/core/evaluatePackageMember.go b/src/core/evaluatePackageMember.go
index a870a53..1f8ca6c 100644
--- a/src/core/evaluatePackageMember.go
+++ b/src/core/evaluatePackageMember.go
@@ -1,6 +1,8 @@
 package core
 
 import (
+	"slices"
+
 	"git.urbach.dev/cli/q/src/errors"
 	"git.urbach.dev/cli/q/src/expression"
 	"git.urbach.dev/cli/q/src/ssa"
@@ -12,10 +14,16 @@ func (f *Function) evaluatePackageMember(pkg *Package, rightText string, expr *e
 	constant, exists := pkg.Constants[rightText]
 
 	if exists {
+		if slices.Contains(f.constantStack, constant) {
+			return nil, errors.New(&CycleDetected{A: f.constantStack[len(f.constantStack)-1].Name, B: constant.Name}, f.File, expr.Source())
+		}
+
+		f.constantStack = append(f.constantStack, constant)
 		tmp := f.File
 		f.File = constant.File
 		v, err := f.evaluateRight(constant.Value)
 		f.File = tmp
+		f.constantStack = f.constantStack[:len(f.constantStack)-1]
 		return v, err
 	}
 
diff --git a/src/core/testdata/CycleDetected2.q b/src/core/testdata/CycleDetected2.q
new file mode 100644
index 0000000..63a51b2
--- /dev/null
+++ b/src/core/testdata/CycleDetected2.q
@@ -0,0 +1,9 @@
+const {
+	x = z
+	y = x
+	z = y
+}
+
+main() {
+	a := x
+}
\ No newline at end of file