diff --git a/contracts/OptionsExchange.sol b/contracts/OptionsExchange.sol
index b24d984..da1d90c 100644
--- a/contracts/OptionsExchange.sol
+++ b/contracts/OptionsExchange.sol
@@ -176,7 +176,7 @@ contract OptionsExchange {
         IERC20 oToken,
         uint256 _amt,
         address payable _transferTo
-    ) public returns (uint256) {
+    ) internal returns (uint256) {
         require(!isETH(oToken), "Can only buy oTokens");
 
         if (!isETH(paymentToken)) {
@@ -224,6 +224,8 @@ contract OptionsExchange {
 
             uint256 ethToTransfer = exchange.getEthToTokenOutputPrice(_amt);
 
+            require(msg.value == ethToTransfer, "Not enough ETH to buy oToken");
+
             emit BuyOTokens(
                 msg.sender,
                 _transferTo,
diff --git a/package-lock.json b/package-lock.json
index 5c697ed..b9ebbae 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -211,6 +211,22 @@
           "integrity": "sha512-S4XzBk5sMB+Rcb/LNcpzXr57VRTxgAvaAEDAl1AwRx27j00hT84O6OkteE7u8UB3NuaaygCRrEpqox4uDOrbdQ==",
           "dev": true
         },
+        "debug": {
+          "version": "2.6.9",
+          "resolved": "https://registry.npmjs.org/debug/-/debug-2.6.9.tgz",
+          "integrity": "sha512-bC7ElrdJaJnPbAP+1EotYvqZsb3ecl5wi6Bfi6BJTUcNowp6cvspg0jXznRTKDjm/E7AdgFBVeAPVMNcKGsHMA==",
+          "requires": {
+            "ms": "2.0.0"
+          }
+        },
+        "scrypt-shim": {
+          "version": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
+          "from": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
+          "requires": {
+            "scryptsy": "^2.1.0",
+            "semver": "^6.3.0"
+          }
+        },
         "uuid": {
           "version": "3.3.2",
           "resolved": "https://registry.npmjs.org/uuid/-/uuid-3.3.2.tgz",
@@ -368,7 +384,6 @@
             "eth-lib": "0.2.7",
             "ethereumjs-common": "^1.3.2",
             "ethereumjs-tx": "^2.1.1",
-            "scrypt-shim": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
             "underscore": "1.9.1",
             "uuid": "3.3.2",
             "web3-core": "1.2.2",
@@ -473,8 +488,7 @@
           "dev": true,
           "requires": {
             "underscore": "1.9.1",
-            "web3-core-helpers": "1.2.2",
-            "websocket": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e"
+            "web3-core-helpers": "1.2.2"
           }
         },
         "web3-shh": {
@@ -504,6 +518,17 @@
             "underscore": "1.9.1",
             "utf8": "3.0.0"
           }
+        },
+        "websocket": {
+          "version": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
+          "from": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
+          "requires": {
+            "debug": "^2.2.0",
+            "es5-ext": "^0.10.50",
+            "nan": "^2.14.0",
+            "typedarray-to-buffer": "^3.1.5",
+            "yaeti": "^0.0.6"
+          }
         }
       }
     },
@@ -553,6 +578,14 @@
         "web3": "1.2.2"
       },
       "dependencies": {
+        "debug": {
+          "version": "2.6.9",
+          "resolved": "https://registry.npmjs.org/debug/-/debug-2.6.9.tgz",
+          "integrity": "sha512-bC7ElrdJaJnPbAP+1EotYvqZsb3ecl5wi6Bfi6BJTUcNowp6cvspg0jXznRTKDjm/E7AdgFBVeAPVMNcKGsHMA==",
+          "requires": {
+            "ms": "2.0.0"
+          }
+        },
         "ethers": {
           "version": "4.0.40",
           "resolved": "https://registry.npmjs.org/ethers/-/ethers-4.0.40.tgz",
@@ -592,6 +625,14 @@
           "integrity": "sha512-4KsaGcPnuhtCZQCxFxN3GVYIhKFPTdLd8PLC552XwbMndtD0cjRFAhDuuydXQ0h08ZfPgzqe6EKHozpuH74iDw==",
           "dev": true
         },
+        "scrypt-shim": {
+          "version": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
+          "from": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
+          "requires": {
+            "scryptsy": "^2.1.0",
+            "semver": "^6.3.0"
+          }
+        },
         "setimmediate": {
           "version": "1.0.4",
           "resolved": "https://registry.npmjs.org/setimmediate/-/setimmediate-1.0.4.tgz",
@@ -799,7 +840,6 @@
             "eth-lib": "0.2.7",
             "ethereumjs-common": "^1.3.2",
             "ethereumjs-tx": "^2.1.1",
-            "scrypt-shim": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
             "underscore": "1.9.1",
             "uuid": "3.3.2",
             "web3-core": "1.2.2",
@@ -912,8 +952,7 @@
           "dev": true,
           "requires": {
             "underscore": "1.9.1",
-            "web3-core-helpers": "1.2.2",
-            "websocket": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e"
+            "web3-core-helpers": "1.2.2"
           }
         },
         "web3-shh": {
@@ -943,6 +982,17 @@
             "underscore": "1.9.1",
             "utf8": "3.0.0"
           }
+        },
+        "websocket": {
+          "version": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
+          "from": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
+          "requires": {
+            "debug": "^2.2.0",
+            "es5-ext": "^0.10.50",
+            "nan": "^2.14.0",
+            "typedarray-to-buffer": "^3.1.5",
+            "yaeti": "^0.0.6"
+          }
         }
       }
     },
@@ -957,6 +1007,22 @@
         "web3": "1.2.2"
       },
       "dependencies": {
+        "debug": {
+          "version": "2.6.9",
+          "resolved": "https://registry.npmjs.org/debug/-/debug-2.6.9.tgz",
+          "integrity": "sha512-bC7ElrdJaJnPbAP+1EotYvqZsb3ecl5wi6Bfi6BJTUcNowp6cvspg0jXznRTKDjm/E7AdgFBVeAPVMNcKGsHMA==",
+          "requires": {
+            "ms": "2.0.0"
+          }
+        },
+        "scrypt-shim": {
+          "version": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
+          "from": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
+          "requires": {
+            "scryptsy": "^2.1.0",
+            "semver": "^6.3.0"
+          }
+        },
         "uuid": {
           "version": "3.3.2",
           "resolved": "https://registry.npmjs.org/uuid/-/uuid-3.3.2.tgz",
@@ -1114,7 +1180,6 @@
             "eth-lib": "0.2.7",
             "ethereumjs-common": "^1.3.2",
             "ethereumjs-tx": "^2.1.1",
-            "scrypt-shim": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
             "underscore": "1.9.1",
             "uuid": "3.3.2",
             "web3-core": "1.2.2",
@@ -1219,8 +1284,7 @@
           "dev": true,
           "requires": {
             "underscore": "1.9.1",
-            "web3-core-helpers": "1.2.2",
-            "websocket": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e"
+            "web3-core-helpers": "1.2.2"
           }
         },
         "web3-shh": {
@@ -1250,6 +1314,17 @@
             "underscore": "1.9.1",
             "utf8": "3.0.0"
           }
+        },
+        "websocket": {
+          "version": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
+          "from": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
+          "requires": {
+            "debug": "^2.2.0",
+            "es5-ext": "^0.10.50",
+            "nan": "^2.14.0",
+            "typedarray-to-buffer": "^3.1.5",
+            "yaeti": "^0.0.6"
+          }
         }
       }
     },
@@ -1266,7 +1341,6 @@
       "version": "4.11.5",
       "resolved": "https://registry.npmjs.org/@types/bn.js/-/bn.js-4.11.5.tgz",
       "integrity": "sha512-AEAZcIZga0JgVMHNtl1CprA/hXX7/wPt79AgR4XqaDt7jyj3QWYw6LPoOiznPtugDmlubUnAahMs2PFxGcQrng==",
-      "dev": true,
       "requires": {
         "@types/node": "*"
       }
@@ -1330,8 +1404,7 @@
     "@types/node": {
       "version": "12.12.14",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-12.12.14.tgz",
-      "integrity": "sha512-u/SJDyXwuihpwjXy7hOOghagLEV1KdAST6syfnOk6QZAMzZuWZqXy5aYYZbh8Jdpd4escVFP0MvftHNDb9pruA==",
-      "dev": true
+      "integrity": "sha512-u/SJDyXwuihpwjXy7hOOghagLEV1KdAST6syfnOk6QZAMzZuWZqXy5aYYZbh8Jdpd4escVFP0MvftHNDb9pruA=="
     },
     "@types/normalize-package-data": {
       "version": "2.4.0",
@@ -2495,7 +2568,6 @@
       "version": "1.1.5",
       "resolved": "https://registry.npmjs.org/bip66/-/bip66-1.1.5.tgz",
       "integrity": "sha1-AfqHSHhcpwlV1QESF9GzE5lpyiI=",
-      "dev": true,
       "requires": {
         "safe-buffer": "^5.0.1"
       }
@@ -3610,7 +3682,6 @@
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/drbg.js/-/drbg.js-1.0.1.tgz",
       "integrity": "sha1-Pja2xCs3BDgjzbwzLVjzHiRFSAs=",
-      "dev": true,
       "requires": {
         "browserify-aes": "^1.0.6",
         "create-hash": "^1.1.2",
@@ -4122,10 +4193,44 @@
       "integrity": "sha1-jZWCAsftuq6Dlwf7pvCf8ydgYhA=",
       "dev": true,
       "requires": {
-        "ethereumjs-abi": "git+https://github.com/ethereumjs/ethereumjs-abi.git#1cfbb13862f90f0b391d8a699544d5fe4dfb8c7b",
         "ethereumjs-util": "^5.1.1"
       },
       "dependencies": {
+        "ethereumjs-abi": {
+          "version": "git+https://github.com/ethereumjs/ethereumjs-abi.git#1cfbb13862f90f0b391d8a699544d5fe4dfb8c7b",
+          "from": "git+https://github.com/ethereumjs/ethereumjs-abi.git#1cfbb13862f90f0b391d8a699544d5fe4dfb8c7b",
+          "requires": {
+            "bn.js": "^4.11.8",
+            "ethereumjs-util": "^6.0.0"
+          },
+          "dependencies": {
+            "ethereumjs-util": {
+              "version": "6.2.0",
+              "resolved": "https://registry.npmjs.org/ethereumjs-util/-/ethereumjs-util-6.2.0.tgz",
+              "integrity": "sha512-vb0XN9J2QGdZGIEKG2vXM+kUdEivUfU6Wmi5y0cg+LRhDYKnXIZ/Lz7XjFbHRR9VIKq2lVGLzGBkA++y2nOdOQ==",
+              "requires": {
+                "@types/bn.js": "^4.11.3",
+                "bn.js": "^4.11.0",
+                "create-hash": "^1.1.2",
+                "ethjs-util": "0.1.6",
+                "keccak": "^2.0.0",
+                "rlp": "^2.2.3",
+                "secp256k1": "^3.0.1"
+              }
+            },
+            "keccak": {
+              "version": "2.1.0",
+              "resolved": "https://registry.npmjs.org/keccak/-/keccak-2.1.0.tgz",
+              "integrity": "sha512-m1wbJRTo+gWbctZWay9i26v5fFnYkOn7D5PCxJ3fZUGUEb49dE1Pm4BREUYCt/aoO6di7jeoGmhvqN9Nzylm3Q==",
+              "requires": {
+                "bindings": "^1.5.0",
+                "inherits": "^2.0.4",
+                "nan": "^2.14.0",
+                "safe-buffer": "^5.2.0"
+              }
+            }
+          }
+        },
         "ethereumjs-util": {
           "version": "5.2.0",
           "resolved": "https://registry.npmjs.org/ethereumjs-util/-/ethereumjs-util-5.2.0.tgz",
@@ -4192,15 +4297,6 @@
         }
       }
     },
-    "ethereumjs-abi": {
-      "version": "git+https://github.com/ethereumjs/ethereumjs-abi.git#1cfbb13862f90f0b391d8a699544d5fe4dfb8c7b",
-      "from": "git+https://github.com/ethereumjs/ethereumjs-abi.git",
-      "dev": true,
-      "requires": {
-        "bn.js": "^4.11.8",
-        "ethereumjs-util": "^6.0.0"
-      }
-    },
     "ethereumjs-account": {
       "version": "2.0.5",
       "resolved": "https://registry.npmjs.org/ethereumjs-account/-/ethereumjs-account-2.0.5.tgz",
@@ -4545,7 +4641,6 @@
       "version": "0.1.6",
       "resolved": "https://registry.npmjs.org/ethjs-util/-/ethjs-util-0.1.6.tgz",
       "integrity": "sha512-CUnVOQq7gSpDHZVVrQW8ExxUETWrnrvXYvYz55wOU8Uj4VCgw56XC2B/fVqQN+f7gmrnRHSLVnFAwsCuNwji8w==",
-      "dev": true,
       "requires": {
         "is-hex-prefixed": "1.0.0",
         "strip-hex-prefix": "1.0.0"
@@ -7698,7 +7793,6 @@
       "version": "2.2.4",
       "resolved": "https://registry.npmjs.org/rlp/-/rlp-2.2.4.tgz",
       "integrity": "sha512-fdq2yYCWpAQBhwkZv+Z8o/Z4sPmYm1CUq6P7n6lVTOdb949CnqA0sndXal5C1NleSVSZm6q5F3iEbauyVln/iw==",
-      "dev": true,
       "requires": {
         "bn.js": "^4.11.1"
       }
@@ -7773,15 +7867,6 @@
       "resolved": "https://registry.npmjs.org/scrypt-js/-/scrypt-js-2.0.3.tgz",
       "integrity": "sha1-uwBAvgMEPamgEqLOqfyfhSz8h9Q="
     },
-    "scrypt-shim": {
-      "version": "github:web3-js/scrypt-shim#be5e616323a8b5e568788bf94d03c1b8410eac54",
-      "from": "github:web3-js/scrypt-shim",
-      "dev": true,
-      "requires": {
-        "scryptsy": "^2.1.0",
-        "semver": "^6.3.0"
-      }
-    },
     "scrypt.js": {
       "version": "0.3.0",
       "resolved": "https://registry.npmjs.org/scrypt.js/-/scrypt.js-0.3.0.tgz",
@@ -7812,7 +7897,6 @@
       "version": "3.7.1",
       "resolved": "https://registry.npmjs.org/secp256k1/-/secp256k1-3.7.1.tgz",
       "integrity": "sha512-1cf8sbnRreXrQFdH6qsg2H71Xw91fCCS9Yp021GnUNJzWJS/py96fS4lHbnTnouLp08Xj6jBoBB6V78Tdbdu5g==",
-      "dev": true,
       "requires": {
         "bindings": "^1.5.0",
         "bip66": "^1.1.5",
@@ -7851,8 +7935,7 @@
     "semver": {
       "version": "6.3.0",
       "resolved": "https://registry.npmjs.org/semver/-/semver-6.3.0.tgz",
-      "integrity": "sha512-b39TBaTSfV6yBrapU89p5fKekE2m/NwnDocOVruQFS1/veMgdzuPcnOM34M6CwxW8jH/lxEa5rBoDeUwu5HHTw==",
-      "dev": true
+      "integrity": "sha512-b39TBaTSfV6yBrapU89p5fKekE2m/NwnDocOVruQFS1/veMgdzuPcnOM34M6CwxW8jH/lxEa5rBoDeUwu5HHTw=="
     },
     "semver-compare": {
       "version": "1.0.0",
@@ -9199,13 +9282,12 @@
           "integrity": "sha512-oqsQXzu+ejJACVHy864WwIyw+oB21nw/pI65/sD95Zi98+/HQzFfNcIFneF1NC4bVF3VNX4YHTNq2I2o97LAiA==",
           "requires": {
             "underscore": "1.9.1",
-            "web3-core-helpers": "1.2.1",
-            "websocket": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e"
+            "web3-core-helpers": "1.2.1"
           },
           "dependencies": {
             "websocket": {
               "version": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
-              "from": "github:web3-js/WebSocket-Node#polyfill/globalThis",
+              "from": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
               "requires": {
                 "debug": "^2.2.0",
                 "es5-ext": "^0.10.50",
@@ -9269,8 +9351,7 @@
       "dependencies": {
         "bignumber.js": {
           "version": "git+https://github.com/frozeman/bignumber.js-nolookahead.git#57692b3ecfc98bbdd6b3a516cb2353652ea49934",
-          "from": "git+https://github.com/frozeman/bignumber.js-nolookahead.git",
-          "dev": true
+          "from": "git+https://github.com/frozeman/bignumber.js-nolookahead.git"
         },
         "crypto-js": {
           "version": "3.1.8",
@@ -9327,11 +9408,16 @@
           "integrity": "sha512-VU6/DSUX93d1fCzBz7WP/SGCQizO1rKZi4Px9j/3yRyfssHyFcZamMw2/sj4E8TlfMXONvZLoforR8B4bRoyTQ==",
           "dev": true,
           "requires": {
-            "bignumber.js": "git+https://github.com/frozeman/bignumber.js-nolookahead.git#57692b3ecfc98bbdd6b3a516cb2353652ea49934",
             "crypto-js": "^3.1.4",
             "utf8": "^2.1.1",
             "xhr2-cookies": "^1.1.0",
             "xmlhttprequest": "*"
+          },
+          "dependencies": {
+            "bignumber.js": {
+              "version": "git+https://github.com/frozeman/bignumber.js-nolookahead.git#57692b3ecfc98bbdd6b3a516cb2353652ea49934",
+              "from": "git+https://github.com/frozeman/bignumber.js-nolookahead.git#57692b3ecfc98bbdd6b3a516cb2353652ea49934"
+            }
           }
         }
       }
@@ -9972,29 +10058,6 @@
         "utf8": "3.0.0"
       }
     },
-    "websocket": {
-      "version": "github:web3-js/WebSocket-Node#905deb4812572b344f5801f8c9ce8bb02799d82e",
-      "from": "github:web3-js/WebSocket-Node#polyfill/globalThis",
-      "dev": true,
-      "requires": {
-        "debug": "^2.2.0",
-        "es5-ext": "^0.10.50",
-        "nan": "^2.14.0",
-        "typedarray-to-buffer": "^3.1.5",
-        "yaeti": "^0.0.6"
-      },
-      "dependencies": {
-        "debug": {
-          "version": "2.6.9",
-          "resolved": "https://registry.npmjs.org/debug/-/debug-2.6.9.tgz",
-          "integrity": "sha512-bC7ElrdJaJnPbAP+1EotYvqZsb3ecl5wi6Bfi6BJTUcNowp6cvspg0jXznRTKDjm/E7AdgFBVeAPVMNcKGsHMA==",
-          "dev": true,
-          "requires": {
-            "ms": "2.0.0"
-          }
-        }
-      }
-    },
     "which": {
       "version": "1.3.1",
       "resolved": "https://registry.npmjs.org/which/-/which-1.3.1.tgz",
diff --git a/package.json b/package.json
index a85b2e2..f459141 100644
--- a/package.json
+++ b/package.json
@@ -39,8 +39,8 @@
     "build": "npm run compile:contracts && npm run compile:types",
     "pretest": "npm run build",
     "test": "truffle test",
-    "test:kovan":"truffle test --network kovan ./test/sell-and-buy.test.ts",
-    "test:ropsten":"truffle test --network ropsten ./test/sell-and-buy.test.ts",
+    "test:kovan": "truffle test --network kovan ./test/sell-and-buy.test.ts",
+    "test:ropsten": "truffle test --network ropsten ./test/sell-and-buy.test.ts",
     "test:rinkeby": "truffle test --network rinkeby ./test/sell-and-buy.test.ts",
     "test:mainnet": "truffle test --network mainnet ./test/sell-and-buy.test.ts",
     "lint:contracts": "solhint 'contracts/**/*.sol'",