diff --git a/go.mod b/go.mod
index fe585e15..74c09cf5 100644
--- a/go.mod
+++ b/go.mod
@@ -48,7 +48,7 @@ require (
 	go.bug.st/relaxed-semver v0.0.0-20190922224835-391e10178d18
 	go.opentelemetry.io/contrib/instrumentation/net/http/httptrace/otelhttptrace v0.14.0 // indirect
 	golang.org/x/crypto v0.0.0-20201208171446-5f87f3452ae9 // indirect
-	golang.org/x/mod v0.4.0 // indirect
+	golang.org/x/mod v0.4.1 // indirect
 	golang.org/x/net v0.0.0-20201209123823-ac852fbbde11 // indirect
 	golang.org/x/sys v0.0.0-20201207223542-d4d67f95c62d // indirect
 	golang.org/x/term v0.0.0-20201210144234-2321bbc49cbf // indirect
diff --git a/go.sum b/go.sum
index 842fef1a..4e09516e 100644
--- a/go.sum
+++ b/go.sum
@@ -1193,6 +1193,8 @@ golang.org/x/mod v0.3.0 h1:RM4zey1++hCTbCVQfnWeKs9/IEsaBLA8vTkd0WVtmH4=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.4.0 h1:8pl+sMODzuvGJkmj2W4kZihvVb5mKm8pB/X44PIQHv8=
 golang.org/x/mod v0.4.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/mod v0.4.1 h1:Kvvh58BN8Y9/lBi7hTekvtMpm07eUZ0ck5pRHpsMWrY=
+golang.org/x/mod v0.4.1/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/net v0.0.0-20180406214816-61147c48b25b/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180816102801-aaf60122140d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
@@ -1383,10 +1385,6 @@ golang.org/x/tools v0.0.0-20200117220505-0cba7a3a9ee9/go.mod h1:TB2adYChydJhpapK
 golang.org/x/tools v0.0.0-20200130002326-2f3ba24bd6e7/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
 golang.org/x/tools v0.0.0-20200203215610-ab391d50b528/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
 golang.org/x/tools v0.0.0-20200308013534-11ec41452d41/go.mod h1:o4KQGtdN14AW+yjsvvwRTJJuXz8XRtIHtEnmAXLyFUw=
-golang.org/x/tools v0.0.0-20201210181237-6d345e82f1d8 h1:Pg9rlomzMhg26WdvwSujvC1Pr2lxOfFfhnQ+/LQcjLw=
-golang.org/x/tools v0.0.0-20201210181237-6d345e82f1d8/go.mod h1:emZCQorbCU4vsT4fOWvOPXz4eW1wZW4PmDk9uLelYpA=
-golang.org/x/tools v0.0.0-20201211185031-d93e913c1a58 h1:1Bs6RVeBFtLZ8Yi1Hk07DiOqzvwLD/4hln4iahvFlag=
-golang.org/x/tools v0.0.0-20201211185031-d93e913c1a58/go.mod h1:emZCQorbCU4vsT4fOWvOPXz4eW1wZW4PmDk9uLelYpA=
 golang.org/x/tools v0.0.0-20201211192254-72fbef54948b h1:8fYBhX5ZQZtb7nVKo58TjndJwMM+cOB1xOnfjgH3uiY=
 golang.org/x/tools v0.0.0-20201211192254-72fbef54948b/go.mod h1:emZCQorbCU4vsT4fOWvOPXz4eW1wZW4PmDk9uLelYpA=
 golang.org/x/xerrors v0.0.0-20190410155217-1f06c39b4373/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/internal/rule/rulefunction/sketch.go b/internal/rule/rulefunction/sketch.go
index a7dcc6fc..bb16a12b 100644
--- a/internal/rule/rulefunction/sketch.go
+++ b/internal/rule/rulefunction/sketch.go
@@ -28,15 +28,20 @@ import (
 
 // SketchNameMismatch checks for mismatch between sketch folder name and primary file name.
 func SketchNameMismatch() (result ruleresult.Type, output string) {
-	for extension := range globals.MainFileValidExtensions {
-		validPrimarySketchFilePath := projectdata.ProjectPath().Join(projectdata.ProjectPath().Base() + extension)
-		exist, err := validPrimarySketchFilePath.ExistCheck()
-		if err != nil {
-			panic(err)
-		}
+	primarySketchFilePrefix := projectdata.ProjectPath().Base()
 
-		if exist {
-			return ruleresult.Pass, ""
+	directoryListing, err := projectdata.ProjectPath().ReadDir()
+	if err != nil {
+		panic(err)
+	}
+	directoryListing.FilterOutDirs()
+
+	for _, filePath := range directoryListing {
+		for extension := range globals.MainFileValidExtensions {
+			if filePath.Base() == primarySketchFilePrefix+extension {
+				// There was a case-sensitive match (paths package's Exist() is not always case-sensitive, so can't be used here).
+				return ruleresult.Pass, ""
+			}
 		}
 	}
 
diff --git a/internal/rule/rulefunction/sketch_test.go b/internal/rule/rulefunction/sketch_test.go
index 3f8b1ef2..0a856534 100644
--- a/internal/rule/rulefunction/sketch_test.go
+++ b/internal/rule/rulefunction/sketch_test.go
@@ -64,7 +64,8 @@ func checkSketchRuleFunction(ruleFunction Type, testTables []sketchRuleFunctionT
 func TestSketchNameMismatch(t *testing.T) {
 	testTables := []sketchRuleFunctionTestTable{
 		{"Valid", "Valid", ruleresult.Pass, ""},
-		{"Mismatch", "NameMismatch", ruleresult.Fail, ""},
+		{"Name Mismatch", "NameMismatch", ruleresult.Fail, ""},
+		{"Case Mismatch", "CaseMismatch", ruleresult.Fail, ""},
 	}
 
 	checkSketchRuleFunction(SketchNameMismatch, testTables, t)
diff --git a/internal/rule/rulefunction/testdata/sketches/CaseMismatch/caseMismatch.ino b/internal/rule/rulefunction/testdata/sketches/CaseMismatch/caseMismatch.ino
new file mode 100644
index 00000000..660bdbcc
--- /dev/null
+++ b/internal/rule/rulefunction/testdata/sketches/CaseMismatch/caseMismatch.ino
@@ -0,0 +1,2 @@
+void setup() {}
+void loop() {}