diff --git a/build/phpstan.neon b/build/phpstan.neon
index 4454a9d73c..97a076fab0 100644
--- a/build/phpstan.neon
+++ b/build/phpstan.neon
@@ -23,6 +23,7 @@ parameters:
 		nodesByStringCountMax: 128
 	checkUninitializedProperties: true
 	checkMissingCallableSignature: true
+	reportPossiblyNonexistentConstantArrayOffset: true
 	excludePaths:
 		- ../tests/*/data/*
 		- ../tests/tmp/*
diff --git a/src/Rules/Functions/PrintfParameterTypeRule.php b/src/Rules/Functions/PrintfParameterTypeRule.php
index d91da4590e..68b79d0f00 100644
--- a/src/Rules/Functions/PrintfParameterTypeRule.php
+++ b/src/Rules/Functions/PrintfParameterTypeRule.php
@@ -8,6 +8,7 @@
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleErrorBuilder;
 use PHPStan\Rules\RuleLevelHelper;
+use PHPStan\ShouldNotHappenException;
 use PHPStan\Type\BooleanType;
 use PHPStan\Type\ErrorType;
 use PHPStan\Type\FloatType;
@@ -144,6 +145,10 @@ public function processNode(Node $node, Scope $scope): array
 					continue;
 				}
 
+				if (!array_key_exists($placeholder->acceptingType, $allowedTypeNameMap)) {
+					throw new ShouldNotHappenException();
+				}
+
 				$errors[] = RuleErrorBuilder::message(
 					sprintf(
 						'Parameter #%d of function %s is expected to be %s by placeholder #%d (%s), %s given.',
diff --git a/src/Type/Php/ArgumentBasedFunctionReturnTypeExtension.php b/src/Type/Php/ArgumentBasedFunctionReturnTypeExtension.php
index b039b62d00..990d54df47 100644
--- a/src/Type/Php/ArgumentBasedFunctionReturnTypeExtension.php
+++ b/src/Type/Php/ArgumentBasedFunctionReturnTypeExtension.php
@@ -6,6 +6,7 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\ShouldNotHappenException;
 use PHPStan\Type\Accessory\NonEmptyArrayType;
 use PHPStan\Type\ArrayType;
 use PHPStan\Type\DynamicFunctionReturnTypeExtension;
@@ -44,6 +45,9 @@ public function isFunctionSupported(FunctionReflection $functionReflection): boo
 
 	public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): ?Type
 	{
+		if (!array_key_exists($functionReflection->getName(), self::FUNCTION_NAMES)) {
+			throw new ShouldNotHappenException();
+		}
 		$argumentPosition = self::FUNCTION_NAMES[$functionReflection->getName()];
 
 		if (!isset($functionCall->getArgs()[$argumentPosition])) {
diff --git a/src/Type/Php/HashFunctionsReturnTypeExtension.php b/src/Type/Php/HashFunctionsReturnTypeExtension.php
index 7798d8f0e8..5ab5eead98 100644
--- a/src/Type/Php/HashFunctionsReturnTypeExtension.php
+++ b/src/Type/Php/HashFunctionsReturnTypeExtension.php
@@ -7,6 +7,7 @@
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Php\PhpVersion;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\ShouldNotHappenException;
 use PHPStan\Type\Accessory\AccessoryLowercaseStringType;
 use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
 use PHPStan\Type\Constant\ConstantBooleanType;
@@ -18,6 +19,7 @@
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
 use PHPStan\Type\TypeUtils;
+use function array_key_exists;
 use function array_map;
 use function count;
 use function hash_algos;
@@ -101,7 +103,11 @@ public function getTypeFromFunctionCall(FunctionReflection $functionReflection,
 			return null;
 		}
 
-		$functionData = self::SUPPORTED_FUNCTIONS[strtolower($functionReflection->getName())];
+		$lowerFunctionName = strtolower($functionReflection->getName());
+		if (!array_key_exists($lowerFunctionName, self::SUPPORTED_FUNCTIONS)) {
+			throw new ShouldNotHappenException();
+		}
+		$functionData = self::SUPPORTED_FUNCTIONS[$lowerFunctionName];
 		if (is_bool($functionData['binary'])) {
 			$binaryType = new ConstantBooleanType($functionData['binary']);
 		} elseif (isset($functionCall->getArgs()[$functionData['binary']])) {
diff --git a/src/Type/Php/JsonThrowTypeExtension.php b/src/Type/Php/JsonThrowTypeExtension.php
index 19cfcbaaea..bb5d21007c 100644
--- a/src/Type/Php/JsonThrowTypeExtension.php
+++ b/src/Type/Php/JsonThrowTypeExtension.php
@@ -8,10 +8,12 @@
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\FunctionReflection;
 use PHPStan\Reflection\ReflectionProvider;
+use PHPStan\ShouldNotHappenException;
 use PHPStan\Type\BitwiseFlagHelper;
 use PHPStan\Type\DynamicFunctionThrowTypeExtension;
 use PHPStan\Type\ObjectType;
 use PHPStan\Type\Type;
+use function array_key_exists;
 use function in_array;
 
 #[AutowiredService]
@@ -50,6 +52,9 @@ public function getThrowTypeFromFunctionCall(
 		Scope $scope,
 	): ?Type
 	{
+		if (!array_key_exists($functionReflection->getName(), self::ARGUMENTS_POSITIONS)) {
+			throw new ShouldNotHappenException();
+		}
 		$argumentPosition = self::ARGUMENTS_POSITIONS[$functionReflection->getName()];
 		if (!isset($functionCall->getArgs()[$argumentPosition])) {
 			return null;
diff --git a/src/Type/Php/ReplaceFunctionsDynamicReturnTypeExtension.php b/src/Type/Php/ReplaceFunctionsDynamicReturnTypeExtension.php
index 7d1242ffea..57e3b76710 100644
--- a/src/Type/Php/ReplaceFunctionsDynamicReturnTypeExtension.php
+++ b/src/Type/Php/ReplaceFunctionsDynamicReturnTypeExtension.php
@@ -7,6 +7,7 @@
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\FunctionReflection;
 use PHPStan\Reflection\ParametersAcceptorSelector;
+use PHPStan\ShouldNotHappenException;
 use PHPStan\Type\Accessory\AccessoryArrayListType;
 use PHPStan\Type\Accessory\AccessoryLowercaseStringType;
 use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
@@ -196,6 +197,10 @@ private function getSubjectType(
 		Scope $scope,
 	): ?Type
 	{
+		if (!array_key_exists($functionReflection->getName(), self::FUNCTIONS_SUBJECT_POSITION)) {
+			throw new ShouldNotHappenException();
+		}
+
 		$argumentPosition = self::FUNCTIONS_SUBJECT_POSITION[$functionReflection->getName()];
 		if (count($functionCall->getArgs()) <= $argumentPosition) {
 			return null;
diff --git a/src/Type/Php/StrCaseFunctionsReturnTypeExtension.php b/src/Type/Php/StrCaseFunctionsReturnTypeExtension.php
index c965f8cd12..5f3b7f9ecb 100644
--- a/src/Type/Php/StrCaseFunctionsReturnTypeExtension.php
+++ b/src/Type/Php/StrCaseFunctionsReturnTypeExtension.php
@@ -6,6 +6,7 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\ShouldNotHappenException;
 use PHPStan\Type\Accessory\AccessoryLowercaseStringType;
 use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
 use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
@@ -19,10 +20,10 @@
 use PHPStan\Type\TypeCombinator;
 use PHPStan\Type\TypeUtils;
 use function array_diff;
+use function array_key_exists;
 use function array_map;
 use function count;
 use function in_array;
-use function is_callable;
 use function mb_check_encoding;
 use const MB_CASE_LOWER;
 use const MB_CASE_UPPER;
@@ -62,14 +63,15 @@ public function getTypeFromFunctionCall(
 		$fnName = $functionReflection->getName();
 		$args = $functionCall->getArgs();
 
-		if (count($args) < self::FUNCTIONS[$fnName]) {
-			return null;
+		if (!array_key_exists($fnName, self::FUNCTIONS)) {
+			throw new ShouldNotHappenException();
 		}
+		$requiredArgs = self::FUNCTIONS[$fnName];
 
-		$argType = $scope->getType($args[0]->value);
-		if (!is_callable($fnName)) {
+		if (count($args) < $requiredArgs) {
 			return null;
 		}
+		$argType = $scope->getType($args[0]->value);
 
 		$modes = [];
 		$keepLowercase = false;
diff --git a/src/Type/Php/StrContainingTypeSpecifyingExtension.php b/src/Type/Php/StrContainingTypeSpecifyingExtension.php
index 2e24c9dcbd..097cad2a63 100644
--- a/src/Type/Php/StrContainingTypeSpecifyingExtension.php
+++ b/src/Type/Php/StrContainingTypeSpecifyingExtension.php
@@ -15,6 +15,7 @@
 use PHPStan\Analyser\TypeSpecifierContext;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\ShouldNotHappenException;
 use PHPStan\Type\Accessory\AccessoryLiteralStringType;
 use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
 use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
@@ -65,7 +66,11 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 		$args = $node->getArgs();
 
 		if (count($args) >= 2) {
-			[$hackstackArg, $needleArg] = self::STR_CONTAINING_FUNCTIONS[strtolower($functionReflection->getName())];
+			$lowerFunctionName = strtolower($functionReflection->getName());
+			if (!array_key_exists($lowerFunctionName, self::STR_CONTAINING_FUNCTIONS)) {
+				throw new ShouldNotHappenException();
+			}
+			[$hackstackArg, $needleArg] = self::STR_CONTAINING_FUNCTIONS[$lowerFunctionName];
 
 			$haystackType = $scope->getType($args[$hackstackArg]->value);
 			$needleType = $scope->getType($args[$needleArg]->value)->toString();