diff --git a/index.js b/index.js
index d32cf967..0687f65c 100755
--- a/index.js
+++ b/index.js
@@ -2,9 +2,6 @@
 // builtin tooling
 const path = require("path")
 
-// external tooling
-const postcss = require("postcss")
-
 // internal tooling
 const joinMedia = require("./lib/join-media")
 const resolveId = require("./lib/resolve-id")
@@ -35,234 +32,253 @@ function AtImport(options) {
 
   options.path = options.path.map(p => path.resolve(options.root, p))
 
-  return function(styles, result) {
-    const state = {
-      importedFiles: {},
-      hashFiles: {},
-    }
-
-    if (styles.source && styles.source.input && styles.source.input.file) {
-      state.importedFiles[styles.source.input.file] = {}
-    }
-
-    if (options.plugins && !Array.isArray(options.plugins)) {
-      throw new Error("plugins option must be an array")
-    }
-
-    return parseStyles(result, styles, options, state, []).then(bundle => {
-      applyRaws(bundle)
-      applyMedia(bundle)
-      applyStyles(bundle, styles)
-    })
-  }
-}
-
-function applyRaws(bundle) {
-  bundle.forEach((stmt, index) => {
-    if (index === 0) return
-
-    if (stmt.parent) {
-      const before = stmt.parent.node.raws.before
-      if (stmt.type === "nodes") stmt.nodes[0].raws.before = before
-      else stmt.node.raws.before = before
-    } else if (stmt.type === "nodes") {
-      stmt.nodes[0].raws.before = stmt.nodes[0].raws.before || "\n"
-    }
-  })
-}
+  return {
+    postcssPlugin: "postcss-import",
+    Once(styles, { result, atRule }) {
+      const state = {
+        importedFiles: {},
+        hashFiles: {},
+      }
 
-function applyMedia(bundle) {
-  bundle.forEach(stmt => {
-    if (!stmt.media.length) return
-    if (stmt.type === "import") {
-      stmt.node.params = `${stmt.fullUri} ${stmt.media.join(", ")}`
-    } else if (stmt.type === "media") stmt.node.params = stmt.media.join(", ")
-    else {
-      const nodes = stmt.nodes
-      const parent = nodes[0].parent
-      const mediaNode = postcss.atRule({
-        name: "media",
-        params: stmt.media.join(", "),
-        source: parent.source,
-      })
+      if (styles.source && styles.source.input && styles.source.input.file) {
+        state.importedFiles[styles.source.input.file] = {}
+      }
 
-      parent.insertBefore(nodes[0], mediaNode)
+      if (options.plugins && !Array.isArray(options.plugins)) {
+        throw new Error("plugins option must be an array")
+      }
 
-      // remove nodes
-      nodes.forEach(node => {
-        node.parent = undefined
+      return parseStyles(result, styles, options, state, []).then(bundle => {
+        applyRaws(bundle)
+        applyMedia(bundle)
+        applyStyles(bundle, styles)
       })
 
-      // better output
-      nodes[0].raws.before = nodes[0].raws.before || "\n"
+      function applyRaws(bundle) {
+        bundle.forEach((stmt, index) => {
+          if (index === 0) return
 
-      // wrap new rules with media query
-      mediaNode.append(nodes)
+          if (stmt.parent) {
+            const before = stmt.parent.node.raws.before
+            if (stmt.type === "nodes") stmt.nodes[0].raws.before = before
+            else stmt.node.raws.before = before
+          } else if (stmt.type === "nodes") {
+            stmt.nodes[0].raws.before = stmt.nodes[0].raws.before || "\n"
+          }
+        })
+      }
 
-      stmt.type = "media"
-      stmt.node = mediaNode
-      delete stmt.nodes
-    }
-  })
-}
+      function applyMedia(bundle) {
+        bundle.forEach(stmt => {
+          if (!stmt.media.length) return
+          if (stmt.type === "import") {
+            stmt.node.params = `${stmt.fullUri} ${stmt.media.join(", ")}`
+          } else if (stmt.type === "media")
+            stmt.node.params = stmt.media.join(", ")
+          else {
+            const nodes = stmt.nodes
+            const parent = nodes[0].parent
+            const mediaNode = atRule({
+              name: "media",
+              params: stmt.media.join(", "),
+              source: parent.source,
+            })
 
-function applyStyles(bundle, styles) {
-  styles.nodes = []
-
-  // Strip additional statements.
-  bundle.forEach(stmt => {
-    if (stmt.type === "import") {
-      stmt.node.parent = undefined
-      styles.append(stmt.node)
-    } else if (stmt.type === "media") {
-      stmt.node.parent = undefined
-      styles.append(stmt.node)
-    } else if (stmt.type === "nodes") {
-      stmt.nodes.forEach(node => {
-        node.parent = undefined
-        styles.append(node)
-      })
-    }
-  })
-}
+            parent.insertBefore(nodes[0], mediaNode)
 
-function parseStyles(result, styles, options, state, media) {
-  const statements = parseStatements(result, styles)
+            // remove nodes
+            nodes.forEach(node => {
+              node.parent = undefined
+            })
 
-  return Promise.resolve(statements)
-    .then(stmts => {
-      // process each statement in series
-      return stmts.reduce((promise, stmt) => {
-        return promise.then(() => {
-          stmt.media = joinMedia(media, stmt.media || [])
+            // better output
+            nodes[0].raws.before = nodes[0].raws.before || "\n"
 
-          // skip protocol base uri (protocol://url) or protocol-relative
-          if (stmt.type !== "import" || /^(?:[a-z]+:)?\/\//i.test(stmt.uri)) {
-            return
-          }
+            // wrap new rules with media query
+            mediaNode.append(nodes)
 
-          if (options.filter && !options.filter(stmt.uri)) {
-            // rejected by filter
-            return
+            stmt.type = "media"
+            stmt.node = mediaNode
+            delete stmt.nodes
           }
-
-          return resolveImportId(result, stmt, options, state)
-        })
-      }, Promise.resolve())
-    })
-    .then(() => {
-      const imports = []
-      const bundle = []
-
-      // squash statements and their children
-      statements.forEach(stmt => {
-        if (stmt.type === "import") {
-          if (stmt.children) {
-            stmt.children.forEach((child, index) => {
-              if (child.type === "import") imports.push(child)
-              else bundle.push(child)
-              // For better output
-              if (index === 0) child.parent = stmt
-            })
-          } else imports.push(stmt)
-        } else if (stmt.type === "media" || stmt.type === "nodes") {
-          bundle.push(stmt)
-        }
-      })
-
-      return imports.concat(bundle)
-    })
-}
-
-function resolveImportId(result, stmt, options, state) {
-  const atRule = stmt.node
-  let sourceFile
-  if (atRule.source && atRule.source.input && atRule.source.input.file) {
-    sourceFile = atRule.source.input.file
-  }
-  const base = sourceFile
-    ? path.dirname(atRule.source.input.file)
-    : options.root
-
-  return Promise.resolve(options.resolve(stmt.uri, base, options))
-    .then(paths => {
-      if (!Array.isArray(paths)) paths = [paths]
-      // Ensure that each path is absolute:
-      return Promise.all(
-        paths.map(file => {
-          return !path.isAbsolute(file) ? resolveId(file, base, options) : file
         })
-      )
-    })
-    .then(resolved => {
-      // Add dependency messages:
-      resolved.forEach(file => {
-        result.messages.push({
-          type: "dependency",
-          plugin: "postcss-import",
-          file: file,
-          parent: sourceFile,
-        })
-      })
+      }
 
-      return Promise.all(
-        resolved.map(file => {
-          return loadImportContent(result, stmt, file, options, state)
+      function applyStyles(bundle, styles) {
+        styles.nodes = []
+
+        // Strip additional statements.
+        bundle.forEach(stmt => {
+          if (stmt.type === "import") {
+            stmt.node.parent = undefined
+            styles.append(stmt.node)
+          } else if (stmt.type === "media") {
+            stmt.node.parent = undefined
+            styles.append(stmt.node)
+          } else if (stmt.type === "nodes") {
+            stmt.nodes.forEach(node => {
+              node.parent = undefined
+              styles.append(node)
+            })
+          }
         })
-      )
-    })
-    .then(result => {
-      // Merge loaded statements
-      stmt.children = result.reduce((result, statements) => {
-        return statements ? result.concat(statements) : result
-      }, [])
-    })
-}
+      }
 
-function loadImportContent(result, stmt, filename, options, state) {
-  const atRule = stmt.node
-  const media = stmt.media
-  if (options.skipDuplicates) {
-    // skip files already imported at the same scope
-    if (state.importedFiles[filename] && state.importedFiles[filename][media]) {
-      return
-    }
-
-    // save imported files to skip them next time
-    if (!state.importedFiles[filename]) state.importedFiles[filename] = {}
-    state.importedFiles[filename][media] = true
-  }
+      function parseStyles(result, styles, options, state, media) {
+        const statements = parseStatements(result, styles)
+
+        return Promise.resolve(statements)
+          .then(stmts => {
+            // process each statement in series
+            return stmts.reduce((promise, stmt) => {
+              return promise.then(() => {
+                stmt.media = joinMedia(media, stmt.media || [])
+
+                // skip protocol base uri (protocol://url) or protocol-relative
+                if (
+                  stmt.type !== "import" ||
+                  /^(?:[a-z]+:)?\/\//i.test(stmt.uri)
+                ) {
+                  return
+                }
+
+                if (options.filter && !options.filter(stmt.uri)) {
+                  // rejected by filter
+                  return
+                }
+
+                return resolveImportId(result, stmt, options, state)
+              })
+            }, Promise.resolve())
+          })
+          .then(() => {
+            const imports = []
+            const bundle = []
+
+            // squash statements and their children
+            statements.forEach(stmt => {
+              if (stmt.type === "import") {
+                if (stmt.children) {
+                  stmt.children.forEach((child, index) => {
+                    if (child.type === "import") imports.push(child)
+                    else bundle.push(child)
+                    // For better output
+                    if (index === 0) child.parent = stmt
+                  })
+                } else imports.push(stmt)
+              } else if (stmt.type === "media" || stmt.type === "nodes") {
+                bundle.push(stmt)
+              }
+            })
 
-  return Promise.resolve(options.load(filename, options)).then(content => {
-    if (content.trim() === "") {
-      result.warn(`${filename} is empty`, { node: atRule })
-      return
-    }
+            return imports.concat(bundle)
+          })
+      }
 
-    // skip previous imported files not containing @import rules
-    if (state.hashFiles[content] && state.hashFiles[content][media]) return
+      function resolveImportId(result, stmt, options, state) {
+        const atRule = stmt.node
+        let sourceFile
+        if (atRule.source && atRule.source.input && atRule.source.input.file) {
+          sourceFile = atRule.source.input.file
+        }
+        const base = sourceFile
+          ? path.dirname(atRule.source.input.file)
+          : options.root
+
+        return Promise.resolve(options.resolve(stmt.uri, base, options))
+          .then(paths => {
+            if (!Array.isArray(paths)) paths = [paths]
+            // Ensure that each path is absolute:
+            return Promise.all(
+              paths.map(file => {
+                return !path.isAbsolute(file)
+                  ? resolveId(file, base, options)
+                  : file
+              })
+            )
+          })
+          .then(resolved => {
+            // Add dependency messages:
+            resolved.forEach(file => {
+              result.messages.push({
+                type: "dependency",
+                plugin: "postcss-import",
+                file: file,
+                parent: sourceFile,
+              })
+            })
 
-    return processContent(result, content, filename, options).then(
-      importedResult => {
-        const styles = importedResult.root
-        result.messages = result.messages.concat(importedResult.messages)
+            return Promise.all(
+              resolved.map(file => {
+                return loadImportContent(result, stmt, file, options, state)
+              })
+            )
+          })
+          .then(result => {
+            // Merge loaded statements
+            stmt.children = result.reduce((result, statements) => {
+              return statements ? result.concat(statements) : result
+            }, [])
+          })
+      }
 
+      function loadImportContent(result, stmt, filename, options, state) {
+        const atRule = stmt.node
+        const media = stmt.media
         if (options.skipDuplicates) {
-          const hasImport = styles.some(child => {
-            return child.type === "atrule" && child.name === "import"
-          })
-          if (!hasImport) {
-            // save hash files to skip them next time
-            if (!state.hashFiles[content]) state.hashFiles[content] = {}
-            state.hashFiles[content][media] = true
+          // skip files already imported at the same scope
+          if (
+            state.importedFiles[filename] &&
+            state.importedFiles[filename][media]
+          ) {
+            return
           }
+
+          // save imported files to skip them next time
+          if (!state.importedFiles[filename]) state.importedFiles[filename] = {}
+          state.importedFiles[filename][media] = true
         }
 
-        // recursion: import @import from imported file
-        return parseStyles(result, styles, options, state, media)
+        return Promise.resolve(options.load(filename, options)).then(
+          content => {
+            if (content.trim() === "") {
+              result.warn(`${filename} is empty`, { node: atRule })
+              return
+            }
+
+            // skip previous imported files not containing @import rules
+            if (state.hashFiles[content] && state.hashFiles[content][media])
+              return
+
+            return processContent(result, content, filename, options).then(
+              importedResult => {
+                const styles = importedResult.root
+                result.messages = result.messages.concat(
+                  importedResult.messages
+                )
+
+                if (options.skipDuplicates) {
+                  const hasImport = styles.some(child => {
+                    return child.type === "atrule" && child.name === "import"
+                  })
+                  if (!hasImport) {
+                    // save hash files to skip them next time
+                    if (!state.hashFiles[content]) state.hashFiles[content] = {}
+                    state.hashFiles[content][media] = true
+                  }
+                }
+
+                // recursion: import @import from imported file
+                return parseStyles(result, styles, options, state, media)
+              }
+            )
+          }
+        )
       }
-    )
-  })
+    },
+  }
 }
 
-module.exports = postcss.plugin("postcss-import", AtImport)
+AtImport.postcss = true
+
+module.exports = AtImport
diff --git a/package.json b/package.json
index 1ad0a695..177c61ff 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,6 @@
     "node": ">=10.0.0"
   },
   "dependencies": {
-    "postcss": "^7.0.1",
     "postcss-value-parser": "^3.2.3",
     "read-cache": "^1.0.0",
     "resolve": "^1.1.7"
@@ -32,10 +31,14 @@
     "eslint-config-i-am-meticulous": "^11.0.0",
     "eslint-plugin-import": "^2.17.1",
     "eslint-plugin-prettier": "^3.0.0",
+    "postcss": "^8.0.0",
     "postcss-scss": "^2.0.0",
     "prettier": "~1.19.1",
     "sugarss": "^2.0.0"
   },
+  "peerDependencies": {
+    "postcss": "^8.0.0"
+  },
   "scripts": {
     "ci": "eslint . && ava",
     "lint": "eslint . --fix",
diff --git a/test/import.js b/test/import.js
index ad36328c..56c6250c 100644
--- a/test/import.js
+++ b/test/import.js
@@ -65,7 +65,12 @@ test("should contain a correct sourcemap", t => {
     .then(result => {
       t.is(
         result.map.toString(),
-        readFileSync("test/sourcemap/out.css.map", "utf8").trim()
+        readFileSync(
+          process.platform === "win32"
+            ? "test/sourcemap/out.css.win.map"
+            : "test/sourcemap/out.css.map",
+          "utf8"
+        ).trim()
       )
     })
 })
diff --git a/test/sourcemap/out.css.win.map b/test/sourcemap/out.css.win.map
new file mode 100644
index 00000000..fa8890c4
--- /dev/null
+++ b/test/sourcemap/out.css.win.map
@@ -0,0 +1 @@
+{"version":3,"sources":["test/sourcemap/imported.css","test/sourcemap/in.css"],"names":[],"mappings":"AAAA;EACE,gBAAgB;AAClB;;ACAA;EACE,UAAU;AACZ","file":"test\\sourcemap\\in.css","sourcesContent":["html {\n  background: blue;\n}\n","@import \"imported.css\";\n\nbody {\n  color: red;\n}\n"]}