diff --git a/package-lock.json b/package-lock.json
index 9f9c560..e4d3a67 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -635,6 +635,15 @@
         "normalize-path": "^2.1.1"
       }
     },
+    "argparse": {
+      "version": "1.0.10",
+      "resolved": "https://registry.npmjs.org/argparse/-/argparse-1.0.10.tgz",
+      "integrity": "sha512-o5Roy6tNG4SL/FOkCAN6RzjiakZS25RLYFrcMttJqbdd8BWrnA+fGz57iN5Pb06pvBGvl5gQ0B48dJlslXvoTg==",
+      "dev": true,
+      "requires": {
+        "sprintf-js": "~1.0.2"
+      }
+    },
     "arr-diff": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/arr-diff/-/arr-diff-4.0.0.tgz",
@@ -957,6 +966,12 @@
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       "dev": true
     },
+    "builtin-modules": {
+      "version": "1.1.1",
+      "resolved": "https://registry.npmjs.org/builtin-modules/-/builtin-modules-1.1.1.tgz",
+      "integrity": "sha1-Jw8HbFpywC9bZaR9+Uxf46J4iS8=",
+      "dev": true
+    },
     "cache-base": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/cache-base/-/cache-base-1.0.1.tgz",
@@ -1327,6 +1342,12 @@
       "integrity": "sha1-9B8cEL5LAOh7XxPaaAdZ8sW/0+I=",
       "dev": true
     },
+    "diff": {
+      "version": "4.0.2",
+      "resolved": "https://registry.npmjs.org/diff/-/diff-4.0.2.tgz",
+      "integrity": "sha512-58lmxKSA4BNyLz+HHMUzlOEpg09FV+ev6ZMe3vJihgdxzgcwZ8VoEEPmALCZG9LmqfVoNMMKpttIYTVG6uDY7A==",
+      "dev": true
+    },
     "diff-sequences": {
       "version": "24.9.0",
       "resolved": "https://registry.npmjs.org/diff-sequences/-/diff-sequences-24.9.0.tgz",
@@ -3451,6 +3472,24 @@
       "integrity": "sha512-RdJUflcE3cUzKiMqQgsCu06FPu9UdIJO0beYbPhHN4k6apgJtifcoCtT9bcxOpYBtpD2kCM6Sbzg4CausW/PKQ==",
       "dev": true
     },
+    "js-yaml": {
+      "version": "3.13.1",
+      "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-3.13.1.tgz",
+      "integrity": "sha512-YfbcO7jXDdyj0DGxYVSlSeQNHbD7XPWvrVWeVUujrQEoZzWJIRrCPoyk6kL6IAjAG2IolMK4T0hNUe0HOUs5Jw==",
+      "dev": true,
+      "requires": {
+        "argparse": "^1.0.7",
+        "esprima": "^4.0.0"
+      },
+      "dependencies": {
+        "esprima": {
+          "version": "4.0.1",
+          "resolved": "https://registry.npmjs.org/esprima/-/esprima-4.0.1.tgz",
+          "integrity": "sha512-eGuFFw7Upda+g4p+QHvnW0RyTX/SVeJBDM/gCtMARO0cLuT2HcEKnTPvhjV6aGeqrCB/sbNop0Kszm0jsaWU4A==",
+          "dev": true
+        }
+      }
+    },
     "jsbn": {
       "version": "0.1.1",
       "resolved": "https://registry.npmjs.org/jsbn/-/jsbn-0.1.1.tgz",
@@ -5030,6 +5069,12 @@
         "extend-shallow": "^3.0.0"
       }
     },
+    "sprintf-js": {
+      "version": "1.0.3",
+      "resolved": "https://registry.npmjs.org/sprintf-js/-/sprintf-js-1.0.3.tgz",
+      "integrity": "sha1-BOaSb2YolTVPPdAVIDYzuFcpfiw=",
+      "dev": true
+    },
     "sshpk": {
       "version": "1.16.1",
       "resolved": "https://registry.npmjs.org/sshpk/-/sshpk-1.16.1.tgz",
@@ -5320,12 +5365,65 @@
         }
       }
     },
+    "tslib": {
+      "version": "1.11.2",
+      "resolved": "https://registry.npmjs.org/tslib/-/tslib-1.11.2.tgz",
+      "integrity": "sha512-tTSkux6IGPnUGUd1XAZHcpu85MOkIl5zX49pO+jfsie3eP0B6pyhOlLXm3cAC6T7s+euSDDUUV+Acop5WmtkVg==",
+      "dev": true
+    },
+    "tslint": {
+      "version": "6.1.2",
+      "resolved": "https://registry.npmjs.org/tslint/-/tslint-6.1.2.tgz",
+      "integrity": "sha512-UyNrLdK3E0fQG/xWNqAFAC5ugtFyPO4JJR1KyyfQAyzR8W0fTRrC91A8Wej4BntFzcvETdCSDa/4PnNYJQLYiA==",
+      "dev": true,
+      "requires": {
+        "@babel/code-frame": "^7.0.0",
+        "builtin-modules": "^1.1.1",
+        "chalk": "^2.3.0",
+        "commander": "^2.12.1",
+        "diff": "^4.0.1",
+        "glob": "^7.1.1",
+        "js-yaml": "^3.13.1",
+        "minimatch": "^3.0.4",
+        "mkdirp": "^0.5.3",
+        "resolve": "^1.3.2",
+        "semver": "^5.3.0",
+        "tslib": "^1.10.0",
+        "tsutils": "^2.29.0"
+      },
+      "dependencies": {
+        "minimist": {
+          "version": "1.2.5",
+          "resolved": "https://registry.npmjs.org/minimist/-/minimist-1.2.5.tgz",
+          "integrity": "sha512-FM9nNUYrRBAELZQT3xeZQ7fmMOBg6nWNmJKTcgsJeaLstP/UODVpGsr5OhXhhXg6f+qtJ8uiZ+PUxkDWcgIXLw==",
+          "dev": true
+        },
+        "mkdirp": {
+          "version": "0.5.5",
+          "resolved": "https://registry.npmjs.org/mkdirp/-/mkdirp-0.5.5.tgz",
+          "integrity": "sha512-NKmAlESf6jMGym1++R0Ra7wvhV+wFW63FaSOFPwRahvea0gMUcGUhVeAg/0BC0wiv9ih5NYPB1Wn1UEI1/L+xQ==",
+          "dev": true,
+          "requires": {
+            "minimist": "^1.2.5"
+          }
+        }
+      }
+    },
     "tslint-config-prettier": {
       "version": "1.18.0",
       "resolved": "https://registry.npmjs.org/tslint-config-prettier/-/tslint-config-prettier-1.18.0.tgz",
       "integrity": "sha512-xPw9PgNPLG3iKRxmK7DWr+Ea/SzrvfHtjFt5LBl61gk2UBG/DB9kCXRjv+xyIU1rUtnayLeMUVJBcMX8Z17nDg==",
       "dev": true
     },
+    "tsutils": {
+      "version": "2.29.0",
+      "resolved": "https://registry.npmjs.org/tsutils/-/tsutils-2.29.0.tgz",
+      "integrity": "sha512-g5JVHCIJwzfISaXpXE1qvNalca5Jwob6FjI4AoPlqMusJ6ftFE7IkkFoMhVLRgK+4Kx3gkzb8UZK5t5yTTvEmA==",
+      "dev": true,
+      "requires": {
+        "tslib": "^1.8.1"
+      }
+    },
     "tunnel-agent": {
       "version": "0.6.0",
       "resolved": "https://registry.npmjs.org/tunnel-agent/-/tunnel-agent-0.6.0.tgz",
diff --git a/package.json b/package.json
index 964a164..4cf3812 100644
--- a/package.json
+++ b/package.json
@@ -40,6 +40,7 @@
     "react": "^16.12.0",
     "react-dom": "^16.12.0",
     "ts-jest": "^24.2.0",
+    "tslint": "^6.1.2",
     "tslint-config-prettier": "^1.18.0",
     "typescript": "^3.7.3"
   },
diff --git a/src/useTimer.ts b/src/useTimer.ts
index 4107369..ee05a1c 100644
--- a/src/useTimer.ts
+++ b/src/useTimer.ts
@@ -47,8 +47,10 @@ export const useTimer = ({
 
     if (isRunning) {
       intervalId = setInterval(() => {
-        setTime(time =>
-          timerType === 'DECREMENTAL' ? time - step : time + step
+        setTime(previousTime =>
+          timerType === 'DECREMENTAL'
+            ? previousTime - step
+            : previousTime + step
         );
       }, interval);
     } else if (intervalId) {