diff --git a/NEWS.md b/NEWS.md
index 2f38e5b181..7758c2a7e6 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -6,6 +6,10 @@
 
 - For the `tikz` engine, the class options of the `standalone` document classs can be specified via the chunk option `engine.opts$classoption` (thanks, @XiangyunHuang, #1985). The default value is `tikz`, i.e., `\documentclass[tikz]{standalone}` is used by default.
 
+## MAJOR CHANGES
+
+- An error is now thrown when an inline code result is not coercible to character. This has always been the assumed behavior but it happens to be different in certain formats with unknown automatic coercion. This is now enforced to prevent any unexpected output. An inline code expression must evaluate to a character vector or an object coercible by `as.character()` (#2006).
+
 ## MINOR CHANGES
 
 - The attribute `data-external="1"` will be added to `<iframe>`s generated by `include_url()` to prevent Pandoc from embedding the URL as base64 data (thanks, @IndrajeetPatil, https://stackoverflow.com/q/67477667/559676).
diff --git a/R/block.R b/R/block.R
index 1d9b578869..c279fd9d61 100644
--- a/R/block.R
+++ b/R/block.R
@@ -528,6 +528,9 @@ inline_exec = function(
   for (i in 1:n) {
     res = hook_eval(code[i], envir)
     if (inherits(res, 'knit_asis')) res = sew(res, inline = TRUE)
+    tryCatch(as.character(res), error = function(e) {
+      stop2("The inline value cannot be coerced to character: ", code[i])
+    })
     d = nchar(input)
     # replace with evaluated results
     stringr::str_sub(input, loc[i, 1], loc[i, 2]) = if (length(res)) {
diff --git a/tests/testit/test-block.R b/tests/testit/test-block.R
new file mode 100644
index 0000000000..cdb32cd149
--- /dev/null
+++ b/tests/testit/test-block.R
@@ -0,0 +1,16 @@
+library(testit)
+
+# see http://stackoverflow.com/q/18992260/559676 for the bug
+assert('inline_exec only accept character result', {
+  block = list(code = "function() 1", input = "inline `r function() 1`")
+  res = xfun::try_silent(inline_exec(block, new.env()))
+  (inherits(res, 'try-error'))
+  block = list(code = "(function() 1)()", input = "inline `r (function() 1)()`")
+  block$location = matrix(c(8,27), ncol = 2, byrow = TRUE)
+  res = inline_exec(block, new.env())
+  (res %==% "inline 1")
+  block = list(code = character(0), input = "no inline")
+  res = inline_exec(block, new.env())
+  (res %==% "no inline")
+})
+