diff --git a/README.md b/README.md
index b4342dfa42f04524ef9f944311fa43e45a830573..839d9eb4074347115b4b2786874d1759e3ec929d 100644
--- a/README.md
+++ b/README.md
@@ -35,13 +35,17 @@ The `spaMM` package was developed first to fit mixed-effect models with spatial
 
 Installing `spaMM` from CRAN is generally straightforward, particularly when installing a compiled version. Installing from source on Windows is also easy when the `Rtools` have been installed. 
 
-Additional steps may be needed on other operating systems, for the required `GSL` library and `nloptr` package (which requires the `NLopt` library), and optionally for the `ROI.plugin.glpk` package (which requires the `Rglpk` package, which itself requires the external `glpk` library)
+Additional steps may be needed on other operating systems, for the required `GSL` library and `nloptr` package (which requires the `NLopt` library, version 2.7), and optionally for the `ROI.plugin.glpk` package (which requires the `Rglpk` package, which itself requires the external `glpk` library)
 
 For **Debian or Ubuntu**, this should typically work:\
 `sudo apt-get install libgmp3-dev`\
 `sudo apt-get install libnlopt-dev`\
 `sudo apt-get install libglpk-dev` \
 
+
+If the installation of `nloptr` or `NLopt` fails, **do read the messages**. They may tell you, for example, that `NLopt` 2.7 is not installed for your system. Further, it may not be available by `apt-get` for your system. If `NLopt` 2.7 is not installed, the `nloptr` installation script tries to compile `NLopt` 2.7 from source, but for that purpose `cmake` version 3.15 (or higher) is required, and you need to make sure that it is installed. The `cmake` installation procedure described [here](https://askubuntu.com/questions/1203635/) may then be useful. 
+
+
 **Mac** users may find [HomeBrew](https://brew.sh/) useful: install it and then run 
 `brew install gsl` and `brew install glpk`. However, my limited experience with it was deceptive. It did not tell
 when no writeable `/usr/local/include` directory existed, preventing the installation of the `GSL`. The alternative installation procedure described [here](https://gist.github.com/TysonRayJones/af7bedcdb8dc59868c7966232b4da903#osx) has then been useful.