diff --git a/lib/hacks/grid-end.js b/lib/hacks/grid-end.js
index 8277f0c00..63f6a4225 100644
--- a/lib/hacks/grid-end.js
+++ b/lib/hacks/grid-end.js
@@ -1,4 +1,5 @@
 let Declaration = require('../declaration')
+let { isPureNumber } = require('../utils')
 
 class GridEnd extends Declaration {
   /**
@@ -26,8 +27,12 @@ class GridEnd extends Declaration {
         startDecl = d
       })
       if (startDecl) {
-        let value = Number(decl.value) - Number(startDecl.value) + ''
-        clonedDecl.value = value
+        if (isPureNumber(startDecl.value)) {
+          let value = Number(decl.value) - Number(startDecl.value) + ''
+          clonedDecl.value = value
+        } else {
+          return undefined
+        }
       } else {
         decl.warn(
           result,
diff --git a/lib/hacks/grid-start.js b/lib/hacks/grid-start.js
index 4628e88be..32cebc10d 100644
--- a/lib/hacks/grid-start.js
+++ b/lib/hacks/grid-start.js
@@ -6,7 +6,7 @@ class GridStart extends Declaration {
    */
   check(decl) {
     let value = decl.value
-    return !value.includes('/') || value.includes('span')
+    return !value.includes('/') && !value.includes('span')
   }
 
   /**
diff --git a/lib/utils.js b/lib/utils.js
index f4e1a32cd..2309e8e2b 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -76,3 +76,18 @@ module.exports.splitSelector = function (selector) {
     })
   })
 }
+
+/**
+ * Return true if a given value only contains numbers.
+ * @param {*} value
+ * @returns {boolean}
+ */
+module.exports.isPureNumber = function (value) {
+  if (typeof value === 'number') {
+    return true
+  }
+  if (typeof value === 'string') {
+    return /^[0-9]+$/.test(value)
+  }
+  return false
+}
diff --git a/test/cases/grid.css b/test/cases/grid.css
index 68ec58175..f4818374d 100644
--- a/test/cases/grid.css
+++ b/test/cases/grid.css
@@ -202,3 +202,9 @@
   grid-template-rows: 1fr;
   grid-template-columns: [content] 1fr;
 }
+
+/** https://github.com/postcss/autoprefixer/issues/1446 */
+.issue-1446 {
+  grid-row-start: span 3;
+  grid-row-end: 5;
+}
diff --git a/test/cases/grid.disabled.css b/test/cases/grid.disabled.css
index e7071fbcf..dc3ba0488 100644
--- a/test/cases/grid.disabled.css
+++ b/test/cases/grid.disabled.css
@@ -208,3 +208,9 @@
   grid-template-rows: 1fr;
   grid-template-columns: [content] 1fr;
 }
+
+/** https://github.com/postcss/autoprefixer/issues/1446 */
+.issue-1446 {
+  grid-row-start: span 3;
+  grid-row-end: 5;
+}
diff --git a/test/cases/grid.out.css b/test/cases/grid.out.css
index 40d36dc95..03f230603 100644
--- a/test/cases/grid.out.css
+++ b/test/cases/grid.out.css
@@ -283,3 +283,9 @@
   -ms-grid-row: 1;
   -ms-grid-column: 2;
 }
+
+/** https://github.com/postcss/autoprefixer/issues/1446 */
+.issue-1446 {
+  grid-row-start: span 3;
+  grid-row-end: 5;
+}
diff --git a/test/utils.test.js b/test/utils.test.js
index e648f5505..58cbe23bd 100644
--- a/test/utils.test.js
+++ b/test/utils.test.js
@@ -111,4 +111,18 @@ test('splits complex selectors into an array', () => {
   ])
 })
 
-test.run()
+test('isPureNumber - number', () => {
+  equal(utils.isPureNumber(42), true)
+})
+
+test('isPureNumber - string', () => {
+  equal(utils.isPureNumber('42'), true)
+  equal(utils.isPureNumber('autoprefixer'), false)
+  equal(utils.isPureNumber(''), false)
+})
+
+test.run('isPureNumber - neither number nor string', () => {
+  equal(utils.isPureNumber({}), false)
+  equal(utils.isPureNumber(undefined), false)
+  equal(utils.isPureNumber(true), false)
+})