Why is libcurl showing as not usable on Mac OS X?

I'm running the configure command to install a particular software package, but it fails when it reaches it's libcurl requirement.

This is the output it gives:

checking for the version of libcurl... 7.34.0checking for libcurl >= version 7.15.2... yeschecking whether libcurl is usable... noconfigure: error: Missing required libcurl >= 7.15.2

So, I have version 7.34 installed, which is greater than the required 7.15.2 - but for some reason it is not usable.. (line 3).

curl --version outputs the following:

> curl --versioncurl 7.34.0 (x86_64-apple-darwin13.0.0) libcurl/7.34.0 OpenSSL/1.0.1e zlib/1.2.8 libidn/1.26Protocols: dict file ftp ftps gopher http https imap imaps pop3 pop3s rtsp smtp smtps telnet tftp Features: IDN IPv6 Largefile NTLM NTLM_WB SSL libz TLS-SRP 

Any idea of what's going on here?